Optical Signal Amplifying Triode And Optical Signal Transfer Method, Optical Signal Relay Device, And Optical Signal Storage Device Using The Same

ABSTRACT

When in an optical signal amplifying triode  10,  light of a second wavelength λ 2 , selected from among light from a first optical amplifier  26,  into which a first input light L 1  of a first wavelength λ 1  and a second input light L 2  of second wavelength λ 2  have been input, and a third input light (control light) L 3 of a third wavelength λ 3  are input into a second optical amplifier  34,  an output light L 4  of the third wavelength λ 3 , selected from among the light output from the second optical amplifier  34,  is light that is modulated in response to the intensity variation of one or both of the first input light L 1  of the first wavelength λ 1  and the third input light L 3  of the third wavelength λ 3  and is an amplified signal, with which the signal gain with respect to the third input light (control light) L 3  of the third wavelength λ 3  is of a magnitude of 2 or more. An optical signal amplifying triode  10,  which can directly perform an optical signal amplification process using control input light, can thus be provided.

TECHNICAL FIELD

This invention concerns (a) an optical signal amplifying triode thatamplifies, controls, or switches optical signals, particularly anoptical signal amplifier favorable for optical communication, opticalimage processing, optical computers, optical measurements, opticalintegrated circuits and other optoelectronic applications enablingadvanced information processing, (b) an optical signal transfer methodand an optical signal relay device for transferring optical signals,which have been propagated via an optical fiber or other predeterminedtransmission path, to other transmission paths indicated by routinginformation included in the optical signals, and (c) an optical signalstorage device that stores optical signals, which have been propagatedvia an optical fiber or other predetermined transmission path, andenables the optical signals to be taken out at any arbitrary time.

BACKGROUND ART

Wide deployment of moving image communication, video distribution, andother new broadband services, using optical fiber communication thatenables broadband and high-speed transmission, is anticipated. However,a functional (signal amplification) element, which, for example,corresponds to a triode transistor in electronics, that is, an opticalfunctional element that performs signal amplification of optical signalsby direct control by other optical signals has not been realized as ofyet.

Thus presently, optical signals that have been transmitted at high speedare converted once into electrical signals, which are then subject toinformation processing in an electronic circuit, and the processedsignals are converted back into and transmitted as optical signals. Alimit is thus placed in the speed of signal processing due to theinability to directly control light by light. It is said that if signalprocessing can be performed on optical signals as they are, parallelprocessing will be enabled and further shortening of the processing timecan be anticipated.

In this regard, the devices described in Document 1 or Document 2 aresimply devices that switch light, in other words, gate switching devicesthat make use of wavelength conversion by Mach-Zehnder opticalinterferometry, and these devices had problems of being weak againsttemperature change and vibration and being strict in terms of settingconditions. Such conventional arts do not disclose anything in regard toarranging an optical signal amplifying triode, which, like a transistorin an electronic circuit, is equipped with a function of using inputlight as control light to obtain signal-amplified output light.

In the field of optical communication enabling broadband, high-speed,and high-capacity signal transmission, it is anticipated thatcommunication, transfer, and distribution of optical signals beperformed without degradation of the properties of high speed and highcapacity. For an optical network based on wavelength divisionmultiplexing (WDM), which is predicted to be constructed in therelatively near future, an optical signal transfer (optical signalrelaying) art, of transferring wavelength division multiplexed opticalsignals, which are a plurality of types of laser light differing inwavelength and which have been transmitted from one optical transmissionpath, to desired optical transmission paths according to wavelength,will be important. In optical signal transfer for transferring anoptical signal train (for example, a packet signal) that has beenpropagated via an optical fiber or other predetermined transmission path(for example, a wavelength bus) to other transmission paths indicated bylabels, tags, or other routing information attached to the opticalsignal train, that is for example, in routing within an optical networkor among optical networks, the high-capacity and high-speedcharacteristics of optical signal transmission must not be degraded androuters, that is, optical signal relay (transfer) devices are requiredto perform transfer processes at high-speed, be high in reliability, andbe compact.

An optical path cross-connection device, such as that described inDocument 3, has been proposed for this purpose. This device is equippedwith a wavelength splitter, which splits a wavelength bus for wavelengthmultiplex transmission link into N wavelength group buses of Gwavelengths each, and a routing processor, which executes a routingprocess on each of the wavelength groups split by the wavelengthsplitter, and is thus arranged to perform the routing process accordingto wavelength group. The routing processor of this optical pathcross-connection device comprises a wavelength converter, which performswavelength conversion according to each wavelength group, and an opticalmatrix switch, which distributes the wavelength-converted light and iscontrolled by a controller. This optical matrix switch is arranged witha mechanically-operated reflecting mirror switch that is positioned atthe intersection of matrix-like optical paths and is alternativelyoperated by the controller to make one wavelength group, among theplurality of wavelength groups, be reflected by the reflecting mirrorswitch and thereby be output to a desired transmission path (paragraph0042, FIG. 10(1)), or has an optical switch, which is alternativelyoperated by the controller, and mesh wiring and is arranged to make onewavelength group, among the plurality of wavelength groups, betransmitted by the optical switch and thereby be output to onetransmission path inside the mesh wiring (paragraph 0043, FIG. 10(2)).

However, with the above-described conventional optical pathcross-connection device, since the routing process is performed by thereflecting mirror switch or the optical switch, the operation of whichis controlled by the controller, the switching operation of thereflecting mirror switch or the optical switch is performed inaccordance with a command signal, which indicates the routingdestination (destination) and is an output that is electronicallyprocessed at the controller. A portion of the optical signal thus had tobe converted to an electrical signal, the destination informationcontained in the electrical signal, that is, a transfer-related signalincluded in a label or tag of a packet had to be extracted, and theoptical signal had to transferred upon electrically controlling theoperation of the reflecting mirror switch or the optical switch inaccordance with the transfer-related signal. Thus, an adequate responsespeed could not be obtained. Also besides the above-described routingprocessor, since a wavelength converter, for performing wavelengthconversion in accordance with the wavelength of the transmission path(wavelength bus) of the transfer destination, is equipped, and such awavelength converter is disposed in addition to the routing processor,the device became large and in some cases, especially when amechanically operated reflecting mirror switch is used, reliabilitycould not be obtained.

Furthermore, in the field of optical communication enabling broadband,high-speed, and high-capacity signal transmission, it is anticipatedthat the identification, multiplexing and splitting, switching, androuting (transfer, distribution) of optical signals (optical data, suchas packet signals) be performed without degrading the characteristics ofbroadband, high speed, and high capacity. In this field of optics,optical signal storage devices, which enable temporary storage andtake-out at desired timings of optical signals, are generally demandedfor optical signal processing systems that process optical signals andare represented, for example, by photonic router systems. This isbecause, just as memories are essential in signal processing in thefield of electronics, optical signal storage devices, referred to asoptical memories or optical buffers, are essential in the field ofoptical signal processing.

In this regard, optical memory devices, such as that described in PatentDocument 1, have been proposed. With this device, a plurality of opticalwaveguide means 105 to 108, respectively arranged from optical fibers ofdifferent length in order to provide a plurality of types of delaytimes, are prepared, and arrangements to pass an optical signal throughany of optical waveguide means 105 to 108 and enable storage of theoptical signal by just the delay time corresponding to the propagationtime in the corresponding optical waveguide means among opticalwaveguide means 105 to 108.

However, with this conventional optical memory device, the storage timeof an optical signal is only determined in advance by the delay timecorresponding to the propagation time in the optical waveguide meansamong optical waveguide means 105 to 108 through which the opticalsignal is made to propagate and the optical signal thus cannot be takenout at a desired timing. The degree of freedom of optical signalprocessing was thus limited and lowering of signal processing efficiencycould not be avoided.

[Document 1] K. E. Stubkjaer, “Semiconductor optical amplifier-basedall-optical gates for high-speed optical processing,” IEEE J. QuantumElectron., vol. 6, no. 6, pp. 1428-1435, November/December 2000.

[Document 2] T. Durhuus, C. Joergensen, B. Mikkelsen, R. J. S. Pedersen,and A. E. Stubkjaer, “All optical wavelength conversion by SOAs in aMach-Zehnder configuration,” IEEE Photon. Technol. Lett., vol. 6, pp.53-55, January 1994.

[Document 3] Japanese Published Unexamined Patent Application No.2002-262319

[Document 4] Japanese Published Unexamined Patent Application No. Hei8-204718

This invention has been made with the above circumstances as abackground, and a first object thereof is to provide an optical signalamplifying triode that can perform an amplification process directly onoptical signals by using control light. A second object is to provide anoptical signal transfer method and an optical signal relay device, withwhich the routing of optical signals can be processed at high speed orby a compact device. A third object is to provide an optical signalstorage device that enables storage of optical signals and taking out ofthe optical signals at an arbitrary time.

Upon carrying out various examinations with the above circumstances asthe background, the present inventor found that in an optical amplifier,such as a semiconductor optical amplifier, a rare-earth-element-dopedfiber amp, etc., spontaneously emitted light of peripheral wavelengthsof an input light of a predetermined wavelength λ₁ vary in intensity inresponse to intensity variations of the input light and this intensityvariation varies inversely with respect to that of the signal intensityvariation of the input light, and found a laser-induced signalenhancement effect, that is, a phenomenon wherein when laser light ofanother wavelength λ₂ within the wavelength range of the spontaneouslyemitted light, that is, within the peripheral wavelength range of theinput light is made incident upon being multiplexed with the inputlight, the overall intensity increases suddenly, with the signal(amplitude) variation of the spontaneously emitted light beingmaintained. The present inventor grasped this phenomenon as a wavelengthconversion function from wavelength λ₁ to λ₂ and conceived an opticaltriode based on a tandem wavelength converter (All-Optical Triode Basedon Tandem Wavelength Converter), with which this wavelength conversionis connected in two stages, and thus came to conceive an optical signalamplifying triode. A first aspect of this invention was made based onthis knowledge.

The present inventor also noted that the optical amplifier of theabove-mentioned optical signal amplifying triode not only has thefunction of wavelength conversion from wavelength λ₁ to λ₂ but is also afunctional element equipped with the wavelength conversion function anda switching function and found that, by multiplexing optical signalswith routing information by amplitude modulation, the functional elementcan be used favorably as a routing device, that is, a transfer devicefor wavelength multiplexed signals. A second and a third aspect of thisinvention was made based on this knowledge.

The present inventor also found that by making an optical amplifier ofan optical signal amplifying triode, which exhibits the above-describedphenomenon, perform the function of wavelength conversion fromwavelength λ₁ to λ₂ and at the same time combining this opticalamplifier with a wavelength splitter that performs distribution todifferent output transmission paths in accordance with the inputwavelengths and interposing this combination in a ring transmission pathin which optical signals circulate, the optical signals that are storedby being made to circulate can be taken out at an arbitrary timing. Afourth aspect of this invention was made based on this knowledge.

DISCLOSURE OF THE INVENTION

First Aspect of the Invention

This aspect of the invention provides an optical signal amplifyingtriode comprising (a) a first semiconductor optical amplifier and asecond semiconductor optical amplifier, each equipping an active layerformed of a pn junction and amplifying, performing wavelength conversionon, and then outputting an optical signal input therein; (b) a firstoptical input means, inputting a first input light of a first wavelengthand a second input light of a second wavelength into the firstsemiconductor optical amplifier; (c) a first wavelength selector,selecting light of the second wavelength from among the light from thefirst semiconductor optical amplifier; (d) a second optical input means,inputting the light of second wavelength that has been selected by thefirst wavelength selector and a third input light of a third wavelengthinto the second semiconductor optical amplifier; and (e) a secondwavelength selector, selecting output light of the third wavelength fromamong the light from the second semiconductor optical amplifier; (f)wherein the output light of the third wavelength is modulated inresponse to the intensity variation of either or both of the first inputlight of the first wavelength and the third input light of the thirdwavelength and the signal gain with respect to the third input light ofthe third wavelength is 2 or more.

With this arrangement, when the light of the second wavelength, selectedfrom the light from the first semiconductor optical amplifier into whichthe first input light of the first wavelength and the second input lightof the second wavelength have been input, and the third input light ofthe third wavelength are input into the second semiconductor opticalamplifier, the output light of the third wavelength, selected from thelight emitted from the second semiconductor optical amplifier, is lightthat is modulated in response to the intensity variation of either orboth of the above-mentioned first input light of the first wavelengthand the third input light of the third wavelength and is an amplifiedsignal with a signal gain of a magnitude of 2 or more with respect tothe above-mentioned third input light of the third wavelength. Anoptical signal amplifying triode, which can perform an amplificationprocess directly on optical signals by using control input light, canthus be provided. Also, since each of the first semiconductor opticalamplifier and the second semiconductor optical amplifier is an opticalamplifier equipped with an active layer comprising a pn junction, theoptical signal amplifying triode is made compact and higher in signalgain.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the first input light of the first wavelengthis modulated light, the second input light of the second wavelength iscontinuous light, the third input light of the third wavelength iscontrol light, and the output light of the third wavelength has a signalwaveform, with which the modulation signal of the first input light isamplified, in the input interval of the control light. In this case, theoutput light of the third wavelength will be amplified light that hasbeen modulated in response to the intensity variation of the first inputlight of the first wavelength in the input interval of the controllight. An optical signal amplifying triode, which can perform aswitching process directly on amplified optical signals by using controlinput light, can thus be provided.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the third wavelength is the same as the firstwavelength. In this case, since the first input light and the thirdinput light, which are the signal input light of the optical signalamplifying triode, and the output light will be of the same wavelength,connection of a plurality of the optical signal amplifying triodes witha common wavelength is enabled and an optical circuit of a high degreeof integration can be arranged using the plurality of the optical signalamplifying triodes.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the signal gain of the output light of thethird wavelength with respect to the control light of the thirdwavelength is 10 or more. The signal gain of the optical signalamplifying triode can then be increased further.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the active layers of the semiconductoroptical amplifiers are arranged from quantum wells, a strained-layersuperlattice, or quantum dots. Since a semiconductor optical amplifier,equipped with an active layer comprising quantum wells or quantum dots,is thus used, high-speed response is enabled. Especially in the casewhere quantum dots are used, a response speed of 100 GHz or more can beobtained. Also, polarization dependence is lessened by the use of astrained-layer superlattice.

Preferably, this aspect of the invention provides the optical signalamplifying triode, further comprising a reflecting means, reflectinglight that has been transmitted through the active layer of anabove-mentioned semiconductor optical amplifier towards thesemiconductor optical amplifier or the other semiconductor opticalamplifier. Since the transmission path in the active layer will then beelongated practically by the reflecting means equipped at one end face,the signal gain can be increased further. The modulation degree of theoutput signal is also increased further by the feedback effect.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein either or each of the first semiconductoroptical amplifier and second semiconductor optical amplifier is equippedat one face thereof with a reflecting means that selectively reflectslight, and the reflection means is optically coupled via a lens toeither or each of the first semiconductor optical amplifier and secondsemiconductor optical amplifier. Here, a microlens can be used favorablyas a converging lens and the input light and the output light aretransmitted via optical fibers.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the reflecting means comprises a firstwavelength selective mirror, which, among the light from the firstsemiconductor optical amplifier, does not reflect the first input lightof the first wavelength but reflects light of the second wavelength tothe second semiconductor optical amplifier; and a second wavelengthselective mirror, which, among the light from the second semiconductoroptical amplifier, does not reflect the second input light of the firstwavelength but reflects light of the third wavelength. In this case, thereflecting means is arranged from the wavelength selective mirror thatfunctions as the first wavelength selector and the wavelength selectivemirror that functions as the second wavelength selector.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein a wavelength selective filter, which does nottransmit light of the first wavelength but transmits light of the secondwavelength, is disposed between one end face of the first semiconductoroptical amplifier and the reflecting means for reflecting light, and awavelength selective filter, which does not transmit light of the secondwavelength but transmits the wavelength of the control light, isdisposed between one end face of the second semiconductor opticalamplifier and the reflecting means for reflecting light. In this case,the first wavelength selector and the second wavelength selector arearranged from the first wavelength selection filter and the secondwavelength selection filter. Also, since the first input light, that is,light of the first wavelength, which is the wavelength of the signallight, is not transmitted by the first wavelength selection filter, evenbetter characteristics are provided.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the reflecting means functions as either orboth of the first wavelength selector and second wavelength selector andthe output light from an above-mentioned semiconductor optical amplifieris input into the other semiconductor optical amplifier by changing oneor both of the incidence angle of the input light and the emission angleof the output light with respect to the reflecting means.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein a plurality of sets of the firstsemiconductor optical amplifier and second semiconductor opticalamplifier are disposed in optical waveguides formed on a semiconductorsubstrate and these sets are integrated as a single chip. In this case,the optical signal amplifying triode can be made to have the smallermonolithic structure of a single integrated chip.

Preferably, this aspect of the invention provides the optical signalamplifying triode, further comprising an optical circulator or adirectional coupler, which makes input light be input into anabove-mentioned semiconductor optical amplifier through one end face ofthe semiconductor optical amplifier and guides light, output from thesemiconductor optical amplifier through the one end face, to an opticalpath that differs from that of the input light. In this case, light thatexits from the other end face of the semiconductor amplifier will notenter a waveguide, which guides light that is to be made incident on theother end face, but will mainly be guided to another output waveguide.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein a wavelength selective mirror or wavelengthselective filter that functions as the first wavelength selector orsecond wavelength selector is disposed inside an optical path and isarranged from any among the group consisting of a grating filter, withwhich the refractive index is varied periodically in the lightpropagation direction, a multilayer film filter, formed by layering aplurality of sets of layers that differ in refractive index, and aphotonic crystal, having a photonic bandgap. In this case, the secondwavelength or the third wavelength is extracted favorably from the lightfrom the first semiconductor optical amplifier or the secondsemiconductor optical amplifier.

Preferably, this aspect of the invention provides the optical signalamplifying triode, wherein the optical signal amplifying triode makes upan optical NAND gate, an optical NOR gate, an optical flip-flop circuit,or an optical operational amplifier. In this case, an optical digitalcircuit or an optical analog circuit can be arranged favorably from theabove-described optical signal amplifying triode.

Also, with the above-described optical signal amplifying triode,components, such as the first semiconductor optical amplifier, thesecond semiconductor optical amplifier, the first wavelength selector,the second wavelength selector, an optical coupler, which multiplexeslight to be input into the above components, etc., may be coupled bymeans of optical waveguides formed on a semiconductor substrate or asubstrate formed of a light transmitting substance, such as a glasssubstrate.

Second Aspect of the Invention

This aspect of the invention provides an optical signal transfer methodof transferring an optical signal train, which has been transmitted viaa predetermined transmission path, to transmission paths, among aplurality of transmission paths, that correspond to routing informationcontained in the optical signal, the optical signal transfer methodcomprising: (a) an input step of inputting the optical signal train, towhich the routing information have been applied, to the main opticalsignal amplifying triode unit; (b) a wavelength conversion step ofsupplying control light of wavelengths, corresponding to signalsindicating the routing information, to the main optical signalamplifying triode unit, and making optical signals of the wavelengths ofthe control light be output from the main optical signal amplifyingtriode unit; and (c) an optical distribution step of inputting theoptical signals, output from the main optical signal amplifying triodeunit, into an optical distributor and distributing the optical signalsaccording to their wavelengths among the plurality of opticaltransmission paths connected to the optical distributor. Amplitudemodulation signals are thus added to the optical signal train as therouting information and the optical signal train is thereby arranged tobe transferred to the destinations indicated by the amplitude modulationsignals.

With this arrangement, the optical signal train, to which the routinginformation have been provided, is input into the main optical signalamplifying triode unit, the control light of the wavelengthscorresponding to the amplitude modulation signals are supplied to themain optical signal amplifying triode unit, optical signals of thewavelengths of the control light are output to the optical distributorfrom the main optical signal amplifying triode unit, and routing iscarried out by the output optical signals being distributed according totheir wavelengths among the plurality of optical transmission pathsconnected to the optical distributor. Since the routing information arethus added to the optical signals, the main optical signal amplifyingtriode unit, having a wavelength conversion function and a switchingfunction, can output optical signals of wavelengths corresponding to therouting information and these signals can then be distributed by theoptical distributor. A routing device, that is, an optical signaltransfer device or optical signal relay device of high speed and compactsize can thus be realized.

Here, the routing information are information, such as IP addresses,source addresses, destination addresses, source routing and other routeinformation, data link layer connection information, etc., which arerelated to the determination of the transfer destinations of opticalsignals.

Preferably, this aspect of the invention provides the optical signaltransfer method, wherein the optical signal train is amplitude modulatedat a modulation degree of no more than 90%. In this case, opticalsignals will not be degraded and the routing information will be addedsecurely to the optical signals.

Preferably, this aspect of the invention provides the optical signaltransfer method, wherein the optical signal train is a packet signal andthe routing information are label information or tag informationprovided at a head portion of the packet signal. Also preferably, theabove-mentioned optical signal train is a packet signal and theabove-mentioned routing information are label information or taginformation provided at a head portion of the packet signal. Labelinformation or tag information can thus be added by amplitude modulationto a label portion or tag portion provided at the head portion of theoptical signal train that makes up the packet signal.

Preferably, this aspect of the invention provides the optical signaltransfer method, wherein in the wavelength conversion step, amplitudemodulation using the control light is applied to the optical signals,output from the main optical signal amplifying triode unit, to add newrouting information to the optical signals. In this case, the transferdestinations can be added-as suited inside a transfer device. Dynamicrouting, by which the transfer route is determined, for example,according to the link state, node state, and traffic state, is thusenabled.

Third Aspect of the Invention

This aspect of the invention provides an optical signal relay device,which, among optical signal transmission networks, transfers an opticalsignal train, having routing information added thereto by amplitudemodulation, from one network to transmission paths, among thetransmission paths of another network, that correspond to the routinginformation contained in the optical signal, comprising: (a) a controllight generator, generating, based on the amplitude modulation signalsof the optical signal train, control light of wavelengths correspondingto the destinations indicated by the amplitude modulation signals; (b) amain optical signal amplifying triode unit, converting the opticalsignal train into an optical signal of the wavelengths of the controllight; and (c) an optical distributor, distributing the optical signal,output from the main optical signal amplifying triode unit, among aplurality of optical transmission paths in accordance with thewavelengths of the optical signal.

With this arrangement, when an optical signal train, having amplitudemodulation signals added as routing information, arrives upon beingtransmitted, control light of wavelengths corresponding to thedestinations indicated by the amplitude modulation signals are generatedby the control light generator based on the amplitude modulation signalsof the optical signal train, the optical signal train is converted intooptical signals of the wavelengths of the above-mentioned control lightby the main optical signal amplifying triode unit, and the opticalsignals output from the main optical signal amplifying triode unit aredistributed among the plurality of optical transmission paths inaccordance with their wavelengths by the optical distributor. Since themain optical signal amplifying triode unit, having a wavelengthconversion function and a switching function, can thus output opticalsignals of wavelengths corresponding to the routing information andthese signals can then be distributed by the optical distributor, arouting device, that is, an optical signal transfer device or opticalsignal relay device of high speed and compact size can be realized.

Preferably, this aspect of the invention provides the optical signalrelay device, further comprising an electronic controller or anall-optical controller, which, in accordance with the amplitudemodulation signals contained in the optical signal, makes control lightof wavelengths, which are in accordance with the routing informationindicated by the amplitude modulation signals, be generated from thecontrol light generator. In this case, since the control light generatoris controlled by the electronic controller or the all-optical controllerto generate the control light of the wavelengths that are in accordancewith the routing information indicated by the amplitude modulationsignals contained in the optical signals, the main optical signalamplifying triode unit, having a wavelength conversion function and aswitching function, can output optical signals of wavelengthscorresponding to the routing information and these signals can then bedistributed by the optical distributor. A routing device, that is, anoptical signal transfer device or optical signal relay device of highspeed and compact size can thus be realized. Also in the case where theelectronic controller is an all-optical controller that opticallyextracts just the amplitude modulation signals contained in the opticalsignals input from the above-mentioned main optical waveguide and makescontrol light of wavelengths corresponding to the address signals begenerated from the control light generator, the merit that theconfidentiality of the optical signals can be secured is provided sinceelectromagnetic waves corresponding to signals besides the addresssignals are not generated.

Preferably, this aspect of the invention provides the optical signalrelay device, further comprising: (a) an optical splitter, branching aportion of the optical signal; (b) a photoelectrical signal converter,converting the optical signal branched by the optical splitter to anelectrical signal and supplying the electrical signal to the electroniccontroller; and (c) an optical delay element, disposed at the downstreamside of the optical splitter and delaying the optical signal that is tobe input into the main optical signal amplifying triode unit uponpassage through optical splitter; and wherein the electronic controllerextracts the amplitude modulation signals contained in the opticalsignal and makes control light of wavelengths, which are in accordancewith the routing information indicated by the amplitude modulationsignals, be generated from the control light generator. Since the mainoptical signal amplifying triode unit, having a wavelength conversionfunction and a switching function, can thus output optical signals ofwavelengths corresponding to the routing information and these signalscan then be distributed by the optical distributor, a routing device,that is, an optical signal transfer device or optical signal relaydevice of high speed and compact size can be realized.

Preferably, this aspect of the invention provides the optical signalrelay device, further comprising: an optical signal storage element,temporarily storing an optical distributed from the optical signaldistributor; and an optical feedback transmission path, feeding back theoptical signal output from the optical signal storage element to theinput side; and wherein when the optical signal is an optical packetsignal that is to be stored temporarily, the electronic controller makesa control optical signal, for converting the optical packet signal to apriorly set storage wavelength, be output, and the optical distributordistributes the optical packet signal, after conversion to the storagewavelength, to the optical signal storage element and makes the opticalpacket signal be stored temporarily in the optical signal storageelement. Here, a merit is provided in that when a plurality of opticalpacket signals that are subject to relay processing are to be output tothe same transmission path, one of the optical packet signals isconverted to the priorly set storage wavelength, the optical wavelengthsplitter distributes the optical packet signal after conversion to thestorage wavelength to the above-mentioned optical signal storageelement, and after being stored in the storage element temporarily, theoptical packet signal is returned to the input side and subject anew tothe relay process.

Preferably, this aspect of the invention provides the optical signalrelay device, wherein the optical signal storage element is equippedwith a plurality of optical fibers, which are disposed in parallel anddiffer in optical propagation length in order to receive optical signalsdistributed by the optical distribution device, the electroniccontroller makes a control optical signal, for converting the opticalpacket signal to be stored temporarily to a priorly set storagewavelength in accordance with the storage time required of the opticalpacket signal, be output, and the optical distributor distributes theoptical packet signal, after conversion to the storage wavelength, to anoptical fiber among the plurality of optical fibers of the opticalsignal storage element and temporarily stores the optical packet signalin the optical fiber. In this case, an optical packet signal istemporarily stored in the process of being propagated inside an opticalfiber, which, among the plurality of optical fibers disposed inparallel, is in accordance with the storage time required of the opticalpacket signal.

Preferably, this aspect of the invention provides the optical signalrelay device, wherein the all-optical controller comprises: an opticalcoupler, branching a portion of the first input light; a continuouslight source, generating continuous light of the same wavelengths as thecontrol light; an optical coupler, multiplexing the continuous lightfrom the continuous light source with the portion of the first inputlight from the optical coupler; and a semiconductor optical amplifier,receiving the light from the optical coupler, outputting control lighthaving the modulation signals contained in the first input light, andbeing of slower response speed than the semiconductor optical amplifier.A controller can thus be arranged in an all-optical manner.

Preferably, this aspect of the invention provides the optical signalrelay device, wherein when output light that are from the main opticalsignal amplifying triode unit are input, the optical distributorselectively distributes the output light, which have been input, tooptical transmission paths, among the plurality of optical transmissionpaths, that correspond to the wavelengths of the control light. Forexample, the optical distributor is an array waveguide grating typewavelength splitter equipped with a first slab waveguide, connected toan input port, a second slab waveguide, connected to a plurality ofoutput ports, and a plurality of array waveguides of different lengths,disposed between the first slab waveguide and the second slab waveguide,and distributes the input light, input into the input port, among theplurality of output ports according to the wavelengths of the inputlight. Such arrangements include a diffraction grating type or prismtype optical distributor, which uses the refraction angles of adiffraction grating or a prism that differ according to wavelength toselectively distribute input light among a plurality of array waveguidesaligned in array form. With such an arrangement, an output light, whichis output from the above-described optical triode and is of a wavelengthcorresponding to the control light, is distributed selectively accordingto wavelength to one of the plurality of branch waveguides.

Fourth Aspect of the Invention

This aspect of the invention provides an optical signal storage device,storing an optical signal input from an input optical transmission pathand enabling taking out of the optical signal at an arbitrary time,comprising: (a) a control light generator, generating control light forconverting the optical signal input from the input optical transmissionpath to wavelengths, which correspond to the transmission destinationscontained in the input signal and are the same as or different from thatof the optical signal; (b) a main optical signal amplifying triode unit,receiving the optical signal that has been input and the control lightand converting the optical signal that has been input to optical signalsof the wavelengths of the control light; (c) an optical distributor,distributing the optical signals, output from the main optical signalamplifying triode unit, in accordance with the wavelengths of theoptical signals; (d) an optical buffer memory element, temporarilystoring an optical signal of a storage wavelength that has beendistributed by the optical distributor; (e) an optical feedbacktransmission path, feeding back the optical signal output from theoptical buffer memory element to the input optical transmission path tore-input the optical signal into the main optical signal amplifyingtriode unit; and (f) an optical signal storage control means, making thecontrol light generator output control light for conversion of theoptical signal, which is repeatedly circulated through the main opticalsignal amplifying triode unit, optical distributor, optical buffermemory element, and the optical feedback transmission path, to an outputwavelength at the main optical signal amplifying triode unit.

With this fourth aspect of this invention, when the optical signal,which is made to circulate repeatedly through the above-mentioned mainoptical signal amplifying triode unit, optical distributor, opticalbuffer memory element, and optical feedback transmission path, isconverted to the output wavelength in the main optical signal amplifyingtriode unit by the optical signal takeout control means, it isdistributed by the distributor to the takeout transmission path based onthe output wavelength and thereby taken out as a time optical signal atan arbitrary timing (takeout time). This takeout transmission path is,for example, prepared for subjecting the optical signal that has beentaken out to a multiplexing process (so-called optical adding process)or a splitting process (so-called optical dropping process).

With this invention of the fourth aspect, the above-mentioned opticalsignal storage control means preferably makes control light, forconverting the wavelength of the optical signal to be input into theabove-mentioned main optical signal amplifying triode unit to a storagewavelength, be generated by the above-mentioned control light generator.With this arrangement, the storage of an input optical signal is startedby the optical signal being converted to the storage wavelength in themain optical signal amplifying triode unit and thereby being made tocirculate through the circulation transmission path, which repeatedlypasses through the above-mentioned main optical signal amplifying triodeunit, optical distributor, optical buffer memory element, and opticalfeedback transmission path.

Preferably, this aspect of the invention provides the optical signalstorage device, further comprising an optical signal gain control means,controlling the optical signal, fed back by the optical feedbacktransmission path, or the control light supplied to the main opticalsignal amplifying triode unit in order to restrain the increase anddecrease of the gain of the optical signal that is circulated. In thiscase, since the attenuation of the optical signal due to circulation isprevented, the gain of the optical signal is kept fixed.

Preferably, this aspect of the invention provides the optical signalstorage device, wherein the main optical signal amplifying triode unitcomprises: a first semiconductor optical amplifier, which performsconversion to a wavelength of a bias light and inversion of the opticalsignal; and a second semiconductor optical amplifier, which performsconversion to the wavelength of the control light and inversion of theoptical signal that has been inverted by the first semiconductor opticalamplifier; and the optical signal gain control means controls theoptical signal, fed back to the optical feedback transmission path,based on the increase or decrease of the gain of the bias lightcontained in the output light from the second semiconductor opticalamplifier. For example, the optical signal that is fed back by theoptical feedback transmission path is attenuated or amplified based onthe increase or decrease of the gain of the bias light. Since theoptical signal that is fed back by the optical feedback transmissionpath is thus prevented from attenuating due to circulation by beingamplified by the optical signal gain control means, the gain of theoptical signal is kept fixed substantially.

Preferably, this aspect of the invention provides the optical signalstorage device, wherein the optical signal gain control means comprises:a first gain control optical amplifier, receiving the bias light and again control light, which is a continuous light of a wavelength thatdiffers from that of the bias light, and outputs a gain control light,which decreases in gain in accompaniment with an increase of the gain ofthe bias light; and a second gain control optical amplifier, receivingthe output light from the first gain control optical amplifier and theoptical signal, which is fed back by the optical feedback transmissionpath, and outputs an optical signal, which increases in gain inaccompaniment with a decrease of the gain of the gain control light. Inthis case, the gain of the optical signal that is circulated for storageis kept fixed by an all-optical process.

Also, preferably either or each of the first gain control opticalamplifier and the second gain control optical amplifier comprises anoptical amplifier formed of a light transmitting medium in which athree-level or four-level energy level system is arranged by the dopingof a rare earth element. Since such an optical amplifier is slow in thecross-gain modulation response time, the signal component of the opticalsignal will be smoothed and the lowering or rising of the gain thereofcan be detected readily.

Preferably, this aspect of the invention provides the optical signalstorage device, wherein the optical signal gain control means comprises:an optical operational controller, which controls the gain of thecontrol light supplied to the main optical signal amplifying triode unitbased on the increase/decrease of the gain of the optical signal fedback by the optical feedback transmission path in order to maintainfixed the gain of the optical signal that is circulated. With thisarrangement, since the optical signal that is output from the mainoptical signal amplifying triode unit is amplified by the all-opticaloperational controller based on the decrease of the gain of the opticalsignal that is fed back and attenuation of the optical signal due tocirculation is thereby prevented, the gain of the optical signal is keptsubstantially fixed.

Preferably, this aspect of the invention provides the optical signalstorage device, further comprising: (a) an electronic controller,controlling the control light generator; (b) a photoelectric signalconverter, converting the optical signal branched by the optic splitterinto an electrical signal and supplying the electrical signal to theelectronic controller; and (c) an optical delay element, disposed at thedownstream side of the optical splitter and delaying the optical signalthat is to be input into the main optical signal amplifying triode unitupon passage through optical splitter; and (d) wherein the electroniccontroller makes the control light, for conversion of the optical signalto the output wavelength, be generated from the control light generatorin response to an output timing indicated by stored signal outputinformation that is supplied from the exterior or is contained in theoptical signal. The optical signal that is stored by circulation canthereby be output by an electronic process in response to the outputtiming indicated by the storage signal output information supplied fromthe exterior or contained in the above-mentioned optical signal.

Preferably, this aspect of the invention provides the optical signalstorage device, further comprising an all-optical operationalcontroller, which makes the control light, for conversion of the opticalsignal to the output wavelength, be generated from the control lightgenerator in response to an output timing indicated by stored signaloutput information that is supplied from the exterior or is contained inthe optical signal. The optical signal that is stored by circulation canthereby be output by an all-optical process in response to the outputtiming indicated by the storage signal output information supplied fromthe exterior or contained in the above-mentioned optical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the arrangement of an opticalsignal amplifying triode of an embodiment of this invention.

FIG. 2 is a perspective view of the external appearance of an opticalamplifier in the embodiment of FIG. 1 in the case where the opticalamplifier is arranged from a semiconductor optical amplifier.

FIG. 3 shows time charts illustrating the actions of the optical signalamplifying triode of FIG. 1 with the waveform of a first input lightbeing indicated in the top stage, the waveforms of control light beingindicated in the middle stage, and the waveforms of output light beingindicated in the bottom stage.

FIG. 4 is a diagram showing the input/output characteristics of theoptical signal amplifying triode of FIG. 1.

FIG. 5 is a diagram showing the frequency characteristics of the outputsignal of the optical signal amplifying triode of FIG. 1.

FIG. 6 shows diagrams of optical flip-flop circuits arranged by theoptical signal amplifying triode of FIG. 1, with FIG. 6(a) showing anoptical flip-flop circuit arranged from a pair of optical NAND gates andFIG. 6(b) showing an optical flip-flop circuit arranged from a pair ofoptical NOR gates.

FIG. 7 shows an optical operational amp circuit arranged by the opticalsignal amplifying triode of FIG. 1.

FIG. 8 is a diagram corresponding to FIG. 1 illustrating the arrangementof another embodiment of an optical signal amplifying triode.

FIG. 9 is a diagram corresponding to FIG. 1 illustrating the arrangementof another embodiment of an optical signal amplifying triode.

FIG. 10 is a diagram illustrating an arrangement wherein the opticalsignal amplifying triode of FIG. 9 is arranged as a monolithicstructure.

FIG. 11 is a diagram corresponding to FIG. 1 illustrating thearrangement of another embodiment of an optical signal amplifying triodewherein a four-terminal type optical circulator is used.

FIG. 12 is a diagram illustrating an arrangement wherein the opticalsignal amplifying triode of FIG. 11 is arranged as a monolithicstructure.

FIG. 13 is a diagram illustrating the arrangement of another embodimentof an optical signal amplifying triode, which is a monolithic structurehaving a V-type optical waveguide that has been epitaxially grown on asemiconductor substrate.

FIG. 14 is a diagram corresponding to FIG. 1 illustrating thearrangement of another embodiment of an optical signal amplifyingtriode.

FIG. 15 is a diagram illustrating the arrangement of another embodimentof an optical signal amplifying triode, which is a monolithic structureequipped with V-type optical waveguides that have been epitaxially grownon a semiconductor substrate.

FIG. 16 is a schematic view illustrating the arrangement of an opticalsignal relay that is an embodiment of a device to which an opticalsignal transfer method is applied.

FIG. 17 is a block diagram illustrating an arrangement example of onerelay among a plurality of relays that make up a portion of the opticalsignal relay device of the embodiment of FIG. 16.

FIG. 18 is a block diagram illustrating the arrangement of the relay ofFIG. 17.

FIG. 19 is a block diagram illustrating an arrangement example of acontrol light generator of FIG. 18.

FIG. 20 is a block diagram illustrating another arrangement example ofthe control light generator of FIG. 18.

FIG. 21 is a block diagram illustrating another arrangement example ofthe control light generator of FIG. 18.

FIG. 22 is a block diagram illustrating an arrangement example of anoptical signal amplifying triode of FIG. 18.

FIG. 23 shows time charts illustrating the actions of the optical signalamplifying triode of FIG. 22 with the waveform of a signal light that isan input light being indicated in the top stage, the waveform of acontrol light being indicated in the middle stage, and the waveform ofan output light being indicated in the bottom stage.

FIG. 24 is a diagram showing the frequency characteristics of theoptical signal amplifying triode of FIG. 22.

FIG. 25 is a diagram illustrating an arrangement example of an opticaldistributor of FIG. 22.

FIG. 26 is a diagram illustrating an arrangement example of an inputoptical signal train of FIG. 23.

FIG. 27 shows time charts that illustrate the input optical signal trainof FIG. 26 using a main signal and an amplitude modulation signal thatmake up the input optical signal train.

FIG. 28 shows time charts that illustrate the actions of a main relayunit of FIG. 18 in regard to the input optical signal train of FIG. 26and illustrate the actions in the case where routing information are notattached.

FIG. 29 shows time charts that illustrate the actions of a main relayunit of FIG. 18 in regard to the input optical signal train of FIG. 26and illustrate the actions in the case where routing information, whichdiffer from the input optical signals, are attached.

FIG. 30 is a diagram corresponding to FIG. 22 illustrating thearrangement of another embodiment of an optical signal amplifyingtriode, wherein control light is generated in an all-optical manner.

FIG. 31 shows time charts illustrating the actions of the optical signalamplifying triode of FIG. 30.

FIG. 32 is a diagram corresponding to FIG. 17 illustrating thearrangement of an optical signal relay, which includes a wavelengthconverter of the embodiment of FIG. 30.

FIG. 33 is a diagram corresponding to FIG. 18 illustrating the principalportion, that is, a relay of another embodiment of an optical signalrelay.

FIG. 34 is a schematic view illustrating the arrangement of anembodiment of an optical signal storage device.

FIG. 35 is a schematic view illustrating the arrangement of anotherembodiment that differs from the optical signal storage device of FIG.34.

FIG. 36 shows time charts illustrating the optical signal storageactions of the optical signal storage device of FIG. 35.

FIG. 37 shows time charts illustrating the optical signal storageactions of the optical signal storage device of FIG. 35 in the casewhere a feedback optical amplifier is not provided.

FIG. 38 is a schematic view illustrating the arrangement of anotherembodiment that differs from the optical signal storage devices of FIG.34 and FIG. 35.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of this invention shall now be described in detail withreference to the drawings.

FIG. 1 through FIG. 15 show embodiments related to an optical signalamplifying triode, and FIG. 1 shows an optical signal amplifying triode10 of one of the embodiments.

In FIG. 1, a first laser light source 12 outputs a first laser light(first input light) L₁ of a first wavelength λ₁ of, for example, 1555nm, and this light is propagated via an optical fiber F₁ that isprovided with a first optical modulator 14. A second laser light source16 continuously outputs a second laser light (second input light) L₂ ofa second wavelength λ₂ of, for example, 1548 nm at a fixed intensity,and this light is propagated via a second optical fiber F₂. A wavelengthvariable semiconductor laser is used for example as the first laserlight source 12, and a semiconductor laser of a single wavelength isused for example as the second laser light source 16. The first opticalmodulator 14 performs, in accordance with an electrical signal or anoptical signal from an unillustrated signal generator, intensitymodulation of the first laser light L₁, which is the transmitted light,so that the light becomes a pulse signal of the frequency of theelectrical signal or the optical signal, such as shown by the waveformof the top stage of FIG. 3. A first optical coupler 18 functions as afirst optical input means that connects the optical fiber F₁ and theoptical fiber F₂ with an optical fiber F₃, overlaps (multiplexes) thefirst laser light L₁ and the second laser light L₂, which have beenpropagated through the optical fiber F₁ and the optical fiber F₂, andinputs the multiplexed light into a first optical amplifier 26 via thethird optical fiber F₃ and a first optical circulator 20.

The first optical amplifier 26 is arranged from a semiconductor opticalamplifier (SOA), such as that shown in FIG. 2.

In FIG. 2, an optical waveguide 26 b, which is formed on a semiconductorsubstrate 26 a arranged from a compound semiconductor, such as indiumphosphide (InP) or gallium arsenide (GaAs), is a multi-layer film of agroup III-V mixed crystal semiconductor, such as InGaAsP, GaInNAs,AlGaInP, etc., that is epitaxially grown on the semiconductor substrate26 a and formed to a predetermined waveguide pattern by photolithographyand is formed, for example, to be a tape-like protrusion ofpredetermined width using photolithography. Since this optical waveguide26 b is formed of a material that is higher in refractive index than thesemiconductor substrate 26 a, it has a function of propagating lightwhile confining the light in the thickness direction. An active layer 26c, arranged from a pn junction, a cap layer, etc., are included in themultilayer film inside the optical waveguide 26 b, and an upperelectrode 26 e is affixed to the top. In the active layer 26 c, anelectron-hole pair is formed by a voltage being applied across a lowersurface electrode 26 f, affixed to the lower surface of thesemiconductor substrate 26 a, and the upper electrode 26 e and anexcitation current being made to flow through the pn junction, and lightthat passes through the active layer 26 c is amplified by an inducedradiation effect. The active layer 26 c is arranged from multiplequantum wells, strained-layer superlattice, or quantum dots. In the caseof multiple quantum wells, six pairs of InGaAs (thickness: 100 Å) andInGaAsP (thickness: 100 Å) layers, which have been latticed-matched bybeing epitaxially grown from an InP semiconductor substrate 26 a, arearranged and a guide layer (2000 Å) with a GRIN structure, which isvaried in composition (refractive index) in a stepwise manner, is formedsuccessively above the active layer 26 c. The device length (opticalpath length) of this active layer 26 c is 600 μm, and it is consideredthat when electrons, which are injected by energy injection by a currentvalue of, for example, 250 mA, are moved into a valence electron band byinduced radiation by transmitted photons, the electrons release opticalenergy and amplify the transmitted light. For example, by this energyinjection by a current value of 250 mA, a gain of approximately 20 dB isobtained for a wavelength of 1555 nm.

A reflecting means 26 d, which is a metal film or a dielectricmultilayer film, etc., that has been processed to reflect light by thesputtering of a metal or a dielectric, is equipped on one end face ofthe first optical amplifier 26, and optical input or optical output isthus performed via the other end face at the side opposite the one endface. The multiplexed light of the first laser light L₁ and the secondlaser light L₂ is thus input into the first optical amplifier 26 via theother end face, and the light reflected by the reflecting means 26 d isagain output via the other end face. Inside the active layer 26 c ofthis first optical amplifier 26, spontaneous light of peripheralwavelengths centered about the wavelength λ₁ of the first laser light L₁is generated by the incidence of the first laser light L₁, and thisspontaneous light increases or decrease in intensity in inverseproportion to the intensity modulation of the first laser light L₁. Whenin this state, the second laser light L₂ of the second wavelength λ₂,which is within the wavelength range of the spontaneous light, istransmitted, this second wavelength λ₂ is reinforced while being made tovary in the same manner as the spontaneous light. That is, light of thesecond wavelength λ₂ is amplified upon being modulated in the samemanner as but inversely in phase with respect to the modulation of thefirst laser light L₁. The first optical amplifier 26, as well as thesecond optical amplifier 34, is thus equipped with cross gain modulationcharacteristics, that is, mutual gain modulation characteristics.

The first optical circulator 20 guides the light output from the firstoptical amplifier 26 not to the third optical fiber F₃ but to a fourthoptical fiber F₄, which is equipped with a first wavelength selector 28.The first wavelength selector 28 is connected to the above-describedfirst optical amplifier 26 and extracts light of the second wavelengthλ₂ of 1548 nm from among the light output from the first opticalamplifier 26. This first wavelength selector 28 functions as an opticalfilter element and, for example, is a fiber grating filter, which isformed by making a portion of the fourth optical fiber F₄ varyperiodically in refractive index in the longitudinal direction bylocalized illumination of ultraviolet rays and selectively transmitslight at a half-width of 1 nm with respect to a central wavelength ofthe second wavelength λ₂. The first wavelength selector 28 may insteadbe arranged from either a multilayer film filter, formed by layering aplurality of layers that differ in refractive index, or a photoniccrystal, having a photonic bandgap.

A second optical coupler 30 functions as a second optical input meansthat multiplexes light of the second wavelength λ₂, which has beenselected by the first wavelength selector 28 from among the light outputfrom first optical amplifier 26, and the third laser light L₃, which isa control light of a third wavelength λ₃ having, for example, a waveformamong those shown in the middle stage of FIG. 3, and inputs themultiplexed light via a fifth optical fiber F₅ and a second opticalcirculator 32 into the second optical amplifier 34, which is arranged inthe same manner as the first optical amplifier 26. At the second opticalamplifier 34, the modulated second wavelength λ₂ is subject to furthermodulation by the control light of the third wavelength λ₃ that iswithin the wavelength range of spontaneous light centered about thesecond wavelength λ₂, and the waveform of the third wavelength λ₃becomes a waveform among those shown in the bottom stage of FIG. 3. Thesecond optical circulator 32 guides the light output from the secondoptical amplifier 34 not to the fifth optical fiber F₅, but to a sixthoptical fiber F₆, which is equipped with a second optical filter element36. The second optical filter 36 selects light of the third wavelengthλ₃from among the light output from the second amplifier 34 and outputsthis light as output light L₄ shown in the bottom stage of FIG. 3. InFIG. 3, the solid line, alternate long and short dash line, and brokenline waveforms of the control light L₃ indicated in the middle stagecorrespond to the solid line, alternate long and short dash line, andbroken line waveforms of the output light L₄ indicated in the bottomstage, and the output light L₄ has a gain of approximately 30 times withrespect to the control light L₃.

FIG. 4 and FIG. 5 illustrate the characteristics of the cross gainmodulation type wavelength conversion actions of the optical signalamplifying triode 10 arranged in the above-described manner. FIG. 4 isan input/output characteristics diagram of the fourth laser light L₄with the signal strength P_(C) of the control light L₃ as a parameter ina two-dimensional coordinate system wherein the abscissa indicates thesignal strength P_(IN) of the first laser light L₁, which is the firstinput light, and the ordinate indicates the signal strength P_(OUT) ofthe fourth laser light L₄, which is the output light. As is clear fromthe Figure, in the same manner as in a triode amplifier, such as atransistor, the signal strength P_(OUT) of the fourth laser light L₄responds to the variation of the signal strength P_(C) of the controllight L₃ with the variation being amplified in the modulation processand responds to the variation of signal strength P_(IN) of the firstlaser light L₁, which is the first input light, with the variation beingamplified in the modulation process. Also, FIG. 5 shows the frequencycharacteristics of the fourth laser light L₄ in a two-dimensionalcoordinate system wherein the abscissa indicates the frequency of thefirst laser light L₁, which is the first input light, and the ordinateindicates the signal modulation degree H (%) of the fourth laser lightL₄, which is the output light. As shown in FIG. 5, lowering of thesignal modulation degree H is not seen up to 5 GHz. This signalmodulation degree H is expressed, for example, by the Equation (1) shownbelow. In this Equation, I_(max) is the maximum value of the opticalsignal and I_(min) is the minimum value of the optical signal. In thecase where quantum dots are used in the active layer 26 c, lowering ofthe signal modulation degree H is not seen in the range of 100 GHz andhigher.H=100×(I _(max) −I _(min))/(I _(max) +I _(min))   1

Experiments by the present inventor have shown that when the controllight L₃ is changed from the third wavelength λ₃ to the first wavelengthλ₁, the output light L₄ of the first wavelength λ₁ is obtained and thesame optical signal amplification effect results as those describedabove are obtained. Also, though in the above, the second wavelength λ₂of the second laser light L₂ is shorter than that of the first laserlight L₁, when the second wavelength λ₂ of the second laser light L₂ ismade longer than that of the first laser light L₁, not only are the sameoptical signal amplification effect results as those described aboveobtained but a further effect that the minimum value, for example, ofthe waveform of the bottom stage of FIG. 3 approaches zero, in otherwords, the effect that the baseline of the output light L₄ approacheszero, like that of the first laser light L₁, is also obtained. Also,when signal modulation is applied to the third input light L₃ of thethird wavelength λ₃ with the first input light L₁ of the firstwavelength λ₁ being a continuous light (bias light) like the secondlaser light L₂ of the second wavelength λ₂, the signal of the thirdinput light L₃, amplified by a gain of 10 or more, is output as theoutput light L₄ of the third wavelength λ₃.

FIG. 6(a) shows a flip-flop circuit 42 arranged from two optical NANDgates 40 to which the above-described optical signal amplifying triode10 is applied, and FIG. 6(b) shows a flip-flop circuit 46 arranged fromtwo optical NOR gates 44. As is well known, a NAND gate and a NOR gatein an electronic circuit are respectively arranged from a plurality oftransistors, and the optical NAND gates 40 and the NOR gates 44 arearranged by providing the above-described optical signal amplifyingtriodes 10 in place of transistors in optical circuits, and theflip-flop circuits 42 and 46 are arranged from a pair of optical NANDgates 40 and a pair of optical NOR gates 44, respectively. With theseflip-flop circuits 42 and 46, information are recorded by means oflight.

FIG. 7 shows an optical operational amp 48 to which the above-describedoptical signal amplifying triode 10 is applied. As is well known, anoperational amp in an electronic circuit is arranged from a plurality oftransistors, and the optical operational amp 48 is arranged by providingthe above-described optical signal amplifying triodes 10 in place oftransistors in an optical circuit.

With the optical signal amplifying triode 10 of FIG. 1, arranged asdescribed above, when light of the second wavelength λ₂, selected fromamong the light from the first optical amplifier 26 into which the firstinput light L₁ of the first wavelength λ₁ and the second input light L₂of the second wavelength λ₂ are input, and the third input light(control light) L₃ of the third wavelength λ₃ are input into the secondoptical amplifier 34, the output light L₄ of the third wavelength λ₃that is selected from among the light output from the second opticalamplifier 34 is light that is modulated in response to the intensityvariation of either or both of the first input light L₁ of the firstwavelength λ₁ and the second input light L₂ of the second wavelength λ₂and is a signal with which the signal gain with respect to the thirdinput light (control light) L₃ of the third wavelength λ₃ is 2 or more.The optical signal amplifying triode 10, which can perform anamplification process on an optical signal directly using control inputlight, can thus be provided.

Also with the optical signal amplifying triode 10 of the presentembodiment, since the first input light L₁ of the first wavelength λ₁ ismodulated light, the second input light L₂ of the second wavelength λ₂is continuous light, the third input light L₃ of the third wavelength λ₃is control light, and the output light L₄ of the third wavelength λ₃has, in the input interval of the control light L₃, a signal waveformwith which the modulated signal of the first input light L₁ isamplified, the output light L₄ of the third wavelength λ₃ is amplifiedlight that is modulated in response to the intensity variation of thefirst input light L₁ of the first wavelength λ₁ in the input interval ofthe control light L₃. The optical signal amplifying triode 10, which canperform a switching process on an amplified optical signal directlyusing control input light, can thus be provided.

Also with the present embodiment, since the first wavelength λ₁ and thethird wavelength λ₃ can be made the same, the first input light L₁,which is the signal input light into the optical signal amplifyingtriode 10, the third input light L₃, and the output light L₄ can be madethe same in wavelength, thus enabling a plurality of the optical signalamplifying triodes 10 to be connected with a common wavelength and anoptical circuit of a high degree of integration to be arranged from aplurality of optical signal amplifying triodes 10.

Also with the present embodiment, the second wavelength λ₂ can be madelonger than the first wavelength λ₁, and in this case, the merit thatthe waveform indicated by the output light L₃, which is the amplifiedlight of the modulated first input light L₁, has a baseline close to thezero level like the baseline of the waveform of the first input light isprovided. The merit of making the modulation degree large is thusprovided.

Also with the present embodiment, since the signal gain of the outputlight L₄ of the third wavelength λ₃ with respect to the control light L₃of the third wavelength λ₃ takes on a value of 10 or more, theamplification function of the optical signal amplifying triode isincreased further and the scope of application thereof is expanded.

Also with the present embodiment, since each of the first opticalamplifier 26 and the second optical amplifier 34 is a semiconductoroptical amplifier equipped with an active layer formed of a pn junction,the optical signal amplifying triode 10, with which the signal gain andthe response speed are increased further, can be obtained.

Also with the present embodiment, since the active layer 26 c of each ofthe first optical amplifier 26 and the second optical amplifier 34 isarranged from quantum wells or quantum dots, the optical signalamplifying triode 10, with which the signal gain and the response speedare increased further, can be obtained. In particular, a response speedof 100 GHz or more can be obtained when quantum dots are used. Also, thepolarization dependence is lessened when a strained-layer superlatticeis used as the active layer.

Also with the present embodiment, since each of the first opticalamplifier 26 and the second optical amplifier 34 has equipped, on oneend face thereof, a mirror or other reflecting means 26 d, formed bymetal deposition, etc., in order to reflect light transmitted via theactive layer 26 c, and the input light is input and the output light istaken out from the other end face, the transmission path in the activelayer 26 c is elongated practically by the mirror or other reflectingmeans 26 d equipped on the one end face and the signal gain is increasedfurther. Also, the modulation degree is increased further by thefeedback effect.

Also with the present embodiment, since the optical circulators 20 and32, into which the input light is input upon transmission via the otherend faces of the first optical amplifier 26 and the second opticalamplifier 34 and which guide the light output through the other endfaces to optical paths that differ from those of the input light, areprovided, the light output from the other end faces of the first opticalamplifier 26 and the second optical amplifier 34 are prevented fromentering the waveguides that guide light to be input into the other endfaces and are mainly guided to other waveguides for output.

Also with the present embodiment, since either or each of the firstwavelength selection element 28 and the second wavelength selectionelement 36 is arranged from a grating filter, with which the refractiveindex of the interior of a waveguide or optical fiber is made to varyperiodically in the light propagation direction, a multilayer filter,formed by layering a plurality of layers that differ in refractiveindex, or a photonic crystal, having a photonic bandgap, the secondwavelength λ₂ or the third wavelength λ₃ is extracted favorably from thelight from the first optical amplifier 26 or the second opticalamplifier 34.

Also, the above-described optical signal amplifying triodes 10 can beused to arrange the optical NAND gate 40, the flip-flop circuit 42,formed of a pair of optical NAND gates 40, or the optical operationalamp 46 and can thereby heighten the functions of an optical integratedcircuit.

Also with the first optical amplifier 26 of the present embodiment,since the second wavelength λ₂ is a wavelength within the wavelengthrange of the peripheral light of the first input light L₁ of the firstwavelength λ₁ and with the second optical amplifier 34, the thirdwavelength λ₃ is a wavelength within the wavelength range of the inputlight of the second wavelength λ₂, a signal of the second wavelength λ₂or the third wavelength λ₃ that is contained in the output light fromthe first optical amplifier 26 or the second amplifier 34 is amplifiedfavorably.

In the case where the reflecting means 26, disposed at the one end faceof the first optical amplifier 26 is arranged from a wavelengthselective reflecting film that transmits light of the first wavelengthλ₁ but reflects light of the second wavelength λ₂, the first wavelengthselector 28 is made unnecessary. When the reflecting means of the secondoptical amplifier 34, arranged in the same manner as the first opticalamplifier 26, is arranged from a wavelength selective reflecting film(wavelength selective mirror) that transmits light of the secondwavelength λ₂ but reflects light of the third wavelength λ₃, the secondwavelength selector 36 is made unnecessary. The above-mentionedwavelength selective reflecting film is formed, for example, of adielectric multilayer film in which dielectric layers that differ inrefractive index are layered in an alternating manner.

Another embodiment shall now be described. In the following description,portions in common to the above-described embodiment shall be providedwith the same symbols and description thereof shall be omitted.

FIG. 8 shows the principal parts of an arrangement example of an opticalsignal amplifying triode 50 of another embodiment of the above-describedoptical signal amplifying triode 10. With the optical signal amplifyingtriode 50 of the present embodiment, an optical signal L_(A) is inputvia a half mirror 51 and a converging lens 52, which serve as the firstoptical input means, into one end face of the first optical amplifier26. Among the light output from the other end face of the first opticalamplifier 26 and via a converging lens 53, light of the first wavelengthλ₁ is transmitted and light of a wavelength λ_(b) of a bias light L₂ isreflected by a wavelength selective mirror 54, which functions as thefirst wavelength selector, and returned to the first optical amplifier26. The light that is output from the one end face of the first opticalamplifier 26 is reflected by the half mirror 51, multiplexed by acontrol light L_(C) by a half mirror 55, which functions as the secondoptical input means, and made incident on one end face of the secondoptical amplifier 34 via a converging lens 56. Among the light outputfrom the other end face of the second optical amplifier 34 and via aconverging lens 57, light of the wavelength λ_(b) of the bias light L₂is transmitted, and the component of the same wavelength as the controllight L_(C) is reflected by a wavelength selective mirror 58, whichfunctions as the second wavelength selector, and returned to the secondoptical amplifier 34. The output light L₃, output from the one end faceof the second amplifier 34 will be the same as that of theabove-described optical signal amplifying triode 10. The wavelengthconverter 50, arranged as described above, provides the same cross gainmodulation type wavelength conversion action and optical amplificationaction as those of the above-described optical signal amplifying triode10. The wavelength selective mirror 58 and the wavelength selectivemirror 54 are optically coupled to the end face of the second opticalamplifier 34 and the end face of the first optical amplifier 26 via theconverging lens 57 and the converging lens 53. The converging lenses 52,53, 56, and 57 are arranged, for example, from microlenses and theoptical signal L_(A), the output signal L₃, etc., are transmitted byoptical fibers. The half mirrors 51 and 55 may be replaced by opticalcouplers or optical circulators.

FIG. 9 shows the principal parts of an arrangement example of an opticalsignal amplifying triode 59 of another embodiment of the above-describedoptical signal amplifying triode 10. The optical signal amplifyingtriode 59 of the present embodiment comprises the first opticalamplifier 26 and the second optical amplifier 34, which are positionedin series, optical couplers 60 and 61, which make the optical signalL_(A) and the bias light L_(b) (wavelength: λ_(b)) be incident on theinner end face of the first optical amplifier 26, a wavelength selectivereflector 62, which, from among the light from the outer end face of thefirst optical amplifier 26, transmits light of the first wavelength λ₁but reflects the component of the wavelength λ_(b) and returns it intothe first optical amplifier 26, a filter 63, which transmits thecomponent of wavelength λ_(b) among the light emitted from the inner endface of the first optical amplifier 26 and makes it incident on theinner end face of the second optical amplifier 34, an optical coupler64, which makes the control light L_(C) incident on the outer end faceof the second optical amplifier 34, and a filter 65, which transmitslight of the same wavelength component as the control light L_(C) amongthe light emitted from the outer end face of the second opticalamplifier 34 and outputs it as the output light L₃. The optical couplers60 and 61 function as the first optical input means, the optical coupler64 functions as the second optical input means, and the reflector 62 andthe filter 65 function as the first wavelength selector and the secondwavelength selector. The wavelength converter 59, arranged as describedabove, provides the same cross gain modulation type wavelengthconversion action and optical amplification action as those of theabove-described optical signal amplifying triode 10. The optical signalof the wavelength λ_(c) of the control light L_(C) is reflected by thefilter 63 and output upon transmission through the filter 65. Theoptical component of the wavelength λ_(b) is not transmitted through thefilter 65. The optical couplers 60 and 61 may be arranged from a singleoptical coupler.

FIG. 10 shows an example where the above-described optical signalamplifying triode 59 is arranged as a monolithic structure of the sametype as the first optical amplifier 26 of monolithic structure that isshown in FIG. 2, that is, as a single chip structure on thesemiconductor substrate 26 a. With this embodiment's optical signalamplifying triode 59 of monolithic structure, the reflector 62, thefilter 63, and the filter 65, each arranged from a grating that isvaried periodically in refractive index, are disposed successively at aposition at the outer side of the first optical amplifier 26, a positionbetween the first optical amplifier 26 and the second optical amplifier34, and at a position at the outer side of the second optical amplifier34. The pair of branch waveguides that are branched from the straightoptical waveguide 26 b correspond to the optical couplers 60 and 61 andthe optical coupler 64.

FIG. 11 shows the principal parts of an arrangement example of anoptical signal amplifying triode 66 of another embodiment of theabove-described optical signal amplifying triode 10. The wavelengthconverter 66 of the present embodiment comprises a pair of reflectingtype first optical amplifier 26 and second optical amplifier 34, afour-terminal optical circulator 67, which is equipped with fourterminals, including a second terminal 67 b and a third terminal 67 cthat are connected to the pair of reflecting type first opticalamplifier 26 and second optical amplifier 34 and which althoughtransmitting light across the four terminals, makes the exit light froma certain terminal differ in optical path from the light incident ontothat terminal, an optical coupler 68, which multiplexes the opticalsignal L_(A) and the bias light L_(b) (wavelength λ_(b)) and makes themultiplexed light incident onto the first terminal (first port) 67 a ofthe four-terminal optical circulator 64, and an optical coupler 69,which multiplexes light of the wavelength λ_(b) that propagates from thereflecting type first optical amplifier 36 to the second port 67 b ofthe four-terminal optical circulator 67 with the control light L_(C) andmakes the multiplexed light incident onto the second optical amplifier34, and makes light of the same wavelength component as the controllight L_(C) be transmitted from the fourth port 67 d of thefour-terminal optical circulator 67. A reflecting film 26 d, whichtransmits light of the first wavelength λ₁ but selectively reflectslight of the second wavelength λ_(b), is disposed on the reflectingsurface of the first optical amplifier 26, and a reflecting film 34 d,which transmits light of the second wavelength λ_(b) but selectivelyreflects light of the same wavelength λ_(c) component as the controllight L_(C), is disposed on the reflecting surface of the second opticalamplifier 34. The optical signal amplifying triode 66, arranged asdescribed above, provides the same cross gain modulation type wavelengthconversion action and optical amplification action as those of theabove-described optical signal amplifying triode 10, and the modulationdegree of the output light L₃ is increased due to passage through thefour-terminal optical circulator 67. This embodiment's optical signalamplifying triode 66 provides the merit of being simple in arrangementin comparison to the optical signal amplifying triode 10 of FIG. 1. Theoptical coupler 69 may be arranged to multiplex the control light L_(C)with light of wavelength λ_(b) that propagates from the third port 67 cof the four-terminal optical circulator 67 to the second opticalamplifying element 34. With the present embodiment, the optical coupler68 and the optical coupler 69 function as the first optical input meansand the second optical input means, and the reflecting films 26 d and 34d function as the first wavelength selector and as the second wavelengthselector.

FIG. 12 shows an example where the above-described optical signalamplifying triode 66 is arranged as a monolithic structure. As with theabove-described arrangements of FIG. 6 and FIG. 10, this optical signalamplifying triode 66 of monolithic structure is equipped with theoptical waveguide 26 b formed on the semiconductor substrate 26 a. Thisoptical waveguide 26 b is provided with a Z-like portion for providingthe same function as the four-terminal optical circulator 67 and branchwaveguides, which are branched from portions of the Z-like portion, forproviding the functions of the optical couplers 68 and 69. At therefraction point of the Z-like portion of the optical waveguide 26 b,the pair of reflecting type first optical amplifier 26 and secondoptical amplifier 34 are arranged in the same manner as those shown inFIG. 2 and FIG. 10 described above. The reflecting films 26 d and 34 dare provided at the outer end faces of the reflecting type first opticalamplifier 26 and second optical amplifier 34.

FIG. 13 shows the principal parts of an arrangement example of anoptical signal amplifying triode 70 of another embodiment of theabove-described optical signal amplifying triode 10. The optical signalamplifying triode 70 of the present embodiment comprises the firstoptical amplifier 26 and the second optical amplifier 34, respectivelyformed by providing a first optical waveguide 72 and a second opticalwaveguide 73 by shaping mixed crystal semiconductor layers, each havinga pn junction layer (active layer) of, for example, GaInNAs grown on arectangular semiconductor substrate 71 of, for example, GaAs, to aV-like shape by photolithography, and providing first optical waveguide72 and second optical waveguide 73 with unillustrated electrodes, awavelength selective reflecting film 74, disposed at an intersectingportion of the first optical waveguide 72 and the second opticalwaveguide 73 at one end face of the rectangular semiconductor substrate71 and reflecting the control light L_(C) and light of the secondwavelength λ_(b) of the bias light L_(b) towards second opticalwaveguide 73 but selectively transmitting light of the first wavelengthλ₁ of the optical signal L_(A), and a wavelength selective reflectingfilm 75, disposed at the output side of the second optical waveguide 73at one end face of the rectangular semiconductor substrate 71 andreflecting light of the second wavelength λ_(b) but transmitting lightof the same wavelength component as the control light L_(C). The opticalsignal L_(A) and bias light L_(b) are multiplexed by an optical coupler76 and then made incident onto an end face of optical waveguide 72, andthe control light L_(C) is made incident into the second waveguide 73from an optical coupler 77, disposed at the outer side of the wavelengthselective reflecting film 75. The optical signal amplifying triode 70,arranged as described above, provides the same cross gain modulationtype wavelength conversion action and optical amplification action asthose of the above-described optical signal amplifying triode 10. Also,since this embodiment's optical signal amplifying triode 70 is arrangedas a single chip by processing mixed crystal semiconductor layers, eachhaving a pn junction layer (active layer) formed of a group III-V mixedcrystal layer, such as GaInNAs, grown on the rectangular semiconductorsubstrate of, for example, GaAs, by photolithography and providingelectrodes, the merit of enabling an arrangement of extremely small sizeis provided. With the present embodiment, the optical couplers 76 and 77function as the first and second optical input means and the wavelengthselective reflecting film 74 and the wavelength selective reflectingfilm 75 function as the first wavelength selector and the secondwavelength selector.

FIG. 14 shows the principal parts of an arrangement example of anoptical signal amplifying triode 78 of another embodiment of theabove-described optical signal amplifying triode 10. With the opticalsignal amplifying triode 78 of the present embodiment, the opticalsignal L_(A) is input into one end face of the first optical amplifier26 via an optical coupler 79, used as a multiplexer, an optical coupler80, used as an optical splitter, and the converging lens 52, and amongthe light output from the other end face of the first optical amplifier26 and via the converging lens 53, the wavelength λ₁ of theabove-mentioned optical signal L_(A) is not transmitted (is absorbed) bya wavelength selective filter 81 and light of the wavelength λ_(b) ofthe bias light is transmitted through the filter 81, reflected by atotal reflecting mirror 82, and returned to the first optical amplifier28. Light that is output from the one end face of the first opticalamplifier 26 is transmitted from the optical coupler 80 to anotheroptical coupler 83 and multiplexed there with the control light L_(C).The light is then made incident on one end face of the second opticalamplifier 34 through an optical coupler 84 and the converging lens 56.Among the light output from the other end face of the second opticalamplifier 34 and through converging lens 57, light of the wavelengthλ_(b) of the bias light is not transmitted (is absorbed) by a wavelengthselective filter 85 and component of the same wavelength λ_(c) ascontrol light L_(C) is transmitted through the filter 85, reflected by atotal reflecting mirror 86, and returned to the second optical amplifier34. The output light L₃, which is output from the one end face of thesecond optical amplifier 34 is output via an optical coupler 84 to anexternal optical distributor 150, such as that described below. Theoptical signal amplifying triode 78, arranged as described above, notonly provides the same cross gain modulation type wavelength conversionaction and optical amplification action as those of the above-describedoptical signal amplifying triode 10 but also provides that merit thatthe characteristics are improved further due to the wavelength λ₁ of theoptical signal L_(A) being absorbed and not transmitted by wavelengthselective filter 81 and the proportion thereof that returns to the firstoptical amplifier 26 side thus being made extremely small. With thepresent embodiment, the optical coupler 79 and the optical coupler 84function as the first optical input means and the second optical inputmeans and the wavelength selective filter 81 and the wavelengthselective filter 85 function as the first wavelength selector and thesecond wavelength selector.

FIG. 15 shows the principal parts of an arrangement example of anotherembodiment of the above-described optical signal amplifying triode 10,which is a monolithic structure wherein a plurality (two in the presentembodiment) of optical signal amplifying triodes 88 are integrated in asingle chip. Each of the plurality of optical signal amplifying triodes88 of the present embodiment comprises the first optical amplifier 26,the second optical amplifier 34, and a third optical amplifier 93,respectively formed by providing a first optical waveguide 90, a secondoptical waveguide 91, and a third optical waveguide 92 by shaping, byphotolithography, mixed crystal semiconductor layers, each having a pnjunction layer (active layer) of, for example, GaInNAs grown on arectangular semiconductor substrate 89 of, for example, GaAs, intostraight lines, extending from one end face to the other end face andforming V-like shapes in adjacent pairs, and by providing the firstoptical waveguide 90, the second optical waveguide 91, and the thirdoptical waveguide 92 with unillustrated electrodes, a wavelengthselective reflecting film (wavelength selective mirror) 94, disposed atan intersecting portion of the first optical waveguide 90 and the secondoptical waveguide 91 and across the output side end face of the thirdoptical waveguide 92 at one end face of the rectangular semiconductorsubstrate 89 and reflecting the control light L_(C) and light of thesecond wavelength λ_(b) of the bias light L_(b) towards the secondoptical waveguide 91 and selectively transmitting the control lightL_(C) and light of the first wavelength λ₁ of the optical signal L_(A),and a wavelength selective reflecting film (wavelength selective mirror)95, disposed at the output side end face of the second optical waveguide91 at one end face of the rectangular semiconductor substrate 89 andtransmitting light of the second wavelength λ_(b) but reflecting lightof the same wavelength component as the control light L_(C) to the thirdoptical waveguide 92. The optical signal L_(A) and bias light L_(b) aremultiplexed by an optical coupler 96 and then made incident onto theinput side end face of the first optical waveguide 90 and the controllight L_(C) is made incident into the second optical waveguide 91 fromthe exterior of the wavelength selective reflecting film 94. Each of theoptical signal amplifying triodes 88, arranged as described above,provides the same cross gain modulation type wavelength conversionaction and optical amplification action as those of the above-describedoptical signal amplifying triode 10. Also, since this embodiment'soptical signal amplifying triodes 88 are arranged as a single chip byprocessing mixed crystal semiconductor layers, each having a pn junctionlayer (active layer) formed of a group III-V mixed crystal layer, suchas GaInNAs, grown on a rectangular semiconductor substrate of, forexample, GaAs, by photolithography and providing electrodes, the meritof enabling the optical signal amplifying triode 10, which can performsignal processing of optical signals of, for example, the 1.3 μm band,to be arranged at an extremely small size is provided. Also with thisembodiment, a circulator is made unnecessary and a higher output isenabled by the three optical amplifiers 26, 34, and 93. With the presentembodiment, the optical coupler 96 functions as the first optical inputmeans, the wavelength selective reflecting film 94 functions as thesecond optical input means and the first wavelength selector, and thewavelength selective reflecting film 95 functions as the secondwavelength selector.

FIG. 16 to FIG. 33 illustrate embodiments related to an optical signaltransfer method and an optical signal router, that is, an optical signalrelay (transfer) device for favorably carrying out the optical signaltransfer method, and with these embodiments, optical communication foradvanced information processing is enabled by the transferring of aoptical signal train, which has been transmitted via a predeterminedtransmission path, to transmission paths, among a plurality oftransmission paths, that correspond to the routing information containedin the optical signal.

FIG. 16 is a diagram that schematically shows an optical signal relay(transfer) device 110 that is disposed between input optical fibersF_(A1) to F_(AM), which are a plurality of transmission paths in oneoptical network, and output optical fibers F_(B1) to F_(BM), which are aplurality of transmission paths in another optical network, andtransfers each of wavelength multiplexed optical signals (laser light)L_(A1) to L_(AM), transmitted via any of the input optical fibers F_(A1)to F_(AM), to a wavelength bus in an output optical fiber among theoutput optical fibers F_(B1) to F_(BM) that has been determined based onrouting information added by amplitude modulation to the optical signal.This optical signal relay device 110 is also referred to as an opticalsignal router.

In FIG. 16, each of the optical signals L_(A1) to L_(AM), transmittedvia any of input optical fibers F_(A1) to F_(AM), is a wavelengthdivision multiplexed (WDM) signal in which optical signals of apredetermined plurality of types of wavelengths are overlapped. Thus forexample, an optical signal L_(A11) of the wavelength λ₁ among a seriesof predetermined wavelengths contained in the optical signal L_(A1) is,in accordance with routing information provided by amplitude modulationbeing applied to a label portion or tag portion thereof, transferred toa wavelength bus in an optical fiber F_(B) among the output opticalfibers F_(B1) to F_(BM), that is, transferred at a wavelength among apredetermined plurality of types, that is, N types of wavelengths λ₁ toλ_(N). Wavelength multiplexed optical signals (laser light) L_(B1) toL_(BM) are transmitted by means of the output optical fibers F_(B1) toF_(BM), respectively.

In addition to M optical splitters (AWGs: Arrayed Waveguide Gratings) S₁to S_(M), which separate the wavelength multiplexed optical signalsL_(A1) to L_(AM), transmitted from the predetermined number, that is,the M input optical fibers F_(A1) to F_(AM), respectively into opticalsignal trains (packets) according to the N types of wavelengths λ₁ toλ_(N), so that, for example, the optical signal L_(A1) is separated intoL_(A11) to L_(A1N), the optical signal relay device 110 comprises Mrelays of first relay R₁ to Mth relay R_(M), which perform wavelengthconversion of the optical signal trains (packets). L_(A11) to L_(A1N) ofN types of wavelengths λ₁ to λ_(N) in accordance with the routinginformation attached to the optical signal trains by amplitudemodulation and perform addition of the prior routing information or newrouting information by amplitude modulation, and M multiplexers (AWGs)T₁ to T_(M), which multiplex the optical signals output from first relayR₁ to Mth relay R_(M) and guide the multiplexed signals to outputoptical fibers F_(B1) to F_(BM).

FIG. 17 is a diagram illustrating the arrangement of a first relay R₁,disposed at a position between the input optical fiber F_(A1) and theoutput optical fiber F_(B1), as a representative example for describingthe arrangement of the first relay R₁ to Mth relay R_(M), which arearranged in the same manner as each other. In FIG. 17, the first relayR₁, is equipped with N main relay units, that is, first main relay unitRB₁₁ to Nth main relay unit RB_(1N), which are arranged in the samemanner as each other, and when the optical splitter S₁ separates thewavelength multiplexed optical signal L_(A1), transmitted from the inputoptical fiber F_(A1), into the optical signal trains (packets) L_(A11)to L_(A1N) in accordance with the N types of wavelengths λ₁ to λ_(N),and these signal trains are input via optical fibers F_(A11) to F_(A1N),the main relay units perform wavelength conversion of the opticalsignals L_(A11) to L_(A1N) in accordance with the routing informationattached to the label portions or tag portions of the optical signals byamplitude modulation and output optical signals upon adding, byamplitude modulation, the same routing information as those up until nowor new routing information. The output signals of any of the wavelengthsof the N types of wavelengths λ₁ to λ_(N), which have been outputrespectively from the first main relay unit RB₁₁ to the Nth main relayunit RB_(1N), are connected to the multiplexer T₁ respectively via N×Ncross-connected fibers F₁₁₁ to F_(NN1) for transmitting optical signalsthat have been branched according to the wavelength and the routinginformation. The output signals from the first main relay unit RB₁₁ tothe Nth main relay unit RB_(1N) are thus transmitted at the desiredwavelengths via the desired output optical fibers among the outputoptical fibers F_(B11) to F_(BN1) to the multiplexer T₁. The main relayunits RB₂₁ to RB_(MN) that make up the other relays R₂ to R_(M) arelikewise connected to the multiplexers T₂ to T_(M) respectively via N×Ncross-connected fibers F₁₁₂ to F_(NM2) . . . N×N cross-connected fibersF_(11M) to F_(NNM). As shown in FIG. 17, the output ends of, forexample, the cross-connected fibers F₁₁₁, F₂₁₁, . . . F_(N11), whichtransmit signals of the same wavelength, that is, the wavelength λ₁, arecoupled together and input via the fiber F_(B11) into the multiplexerT₁. The output ends of the cross-connected fibers F_(1N1), F_(2N1), . .. F_(NN1), which transmit signals of wavelength λ_(N), are coupledtogether and input via the fiber F_(BN1) into the multiplexer T₁.

The optical splitter S₁ is a well-known optical splitting circuit thatis arranged, for example, using an angular dispersion element, such as adiffraction grating, prism, etc., a wavelength selectivereflecting/transmitting film, such as an interference filter arrangedfrom a dielectric multilayer film, etc., or an optical waveguide typeoptical splitting circuit, etc. The multiplexer T₁ is arranged, forexample, from an optical directional coupling circuit, havingmicrolenses as principal components, a distribution coupling typeoptical multiplexing coupler, wherein portions of a plurality of opticalfibers disposed in parallel are coupled together locally, or aconcentrated coupling type optical multiplexing coupler that makes useof multiple reflection at the inner walls of a rectangular tube ormixing in a flat plate.

Also, the first main relay unit RB₁₁ is arranged, for example, as shownin FIG. 18. In FIG. 18, the optical signal L_(A11), input from theoptical splitter S₁ via the optical fiber F_(A11), is connectedsuccessively to a first optical coupler 114, which functions as anoptical splitter/coupler, an optical delay element 116, and a cross gainmodulation type wavelength converter (optical switching device or mainoptical signal amplifying triode unit) 118. The first optical coupler114 is arranged from a branching circuit, having optical fibers asprincipal components, or a branching circuit, having microlenses asprincipal components, etc. A branching circuit having optical fibers asprincipal components is arranged, for example, by putting a pair ofoptical fibers into a parallel state of mutual close contact with eachother or into a state of mutual close contact by twisting the fibersmutually in spiral form over a predetermined interval and disposing areflecting film that can transmit and reflect at a branching point ofthe fibers. With a branching circuit having microlenses as principalcomponents, for example, light that has been formed into a parallel beamby means of a converging rod lens is branched using a wedge typerefracting surface or reflecting surface. Since this first opticalcoupler 114 is equipped with bidirectionality, that is, withreversibility, it functions as a multiplexer, which, when opticalsignals are propagated in an opposite direction, multiplexes the opticalsignals and makes the multiplexed signal propagate in the oppositedirection inside a first optical fiber 112.

The optical delay element 116 delays an optical signal, transmittedinside the above-mentioned optical fiber F_(A11) by just a predeterminedamount of time and is arranged, for example, by winding an optical fiberof predetermined length and thereby providing a propagation distance todelay the optical signal by the propagation time it takes for theoptical signal to propagate across the predetermined propagationdistance. The delay time of the optical delay element 116 is determinedby experiment in advance so that the optical signal to be subject towavelength conversion inside the wavelength converter 118 will besynchronized with the control light that indicates the transmissiondestination of the optical signal.

The branched optical signal that is branched by the first opticalcoupler 114 from the optical signal inside the optical fiber F_(A11) issupplied to an electronic controller 124, via an optical fiber 120 and aphotoelectrical signal converter 122 connected thereto. The electroniccontroller 124 is, for example, arranged from a so-called microcomputer,wherein a CPU processes the input signal in accordance with a programstored in advance in a ROM and using the temporary storage function of aRAM. Based on a code signal, that is, routing information indicated byamplitude modulation and contained in the optical signal transmitted viathe optical fiber 120, the electronic controller 124 supplies awavelength command signal, corresponding to the routing information forrouting the optical signal, to a control light generator 126. Since theelectronic controller 124 extracts, for example, just the amplitudemodulation signal contained in the optical signal L_(A11) input from theoptical fiber 120 and makes the control light L_(C), which is inaccordance with the wavelength corresponding to the routing informationindicated by the amplitude modulation, be generated from the controllight generator 126, electromagnetic waves corresponding to signalsbesides the address signal are not generated.

The control light generator 126 has a control light source that outputsthe control light L_(C) of a plurality of priorly set types ofwavelengths λ_(c) and, in accordance with the command signal from theelectronic controller 124, that is, in accordance with the wavelengthcommand signal selected in accordance with the branching informationcontained in the optical signal L₁, supplies control light L_(C) ofwavelengths λ_(c) corresponding to the branching information to thewavelength converter 118. The control light generator 126 generates inan alternative or selective manner, the control light L_(C) of aplurality of types, for example, N types of wavelengths λ_(c1), λ_(c2),λ_(c3), . . . λ_(cN) in correspondence to the number of wavelength busesinside the transfer destination output optical fibers F_(B1) to F_(BM).FIG. 19, FIG. 20, and FIG. 21 respectively illustrate arrangementexamples of the control light generator 126.

In FIG. 19, the control light generator 126 comprises a plurality oflaser light sources 126 _(L1) to 126 _(Ln), which are the controlsources that output light, each of a single wavelength and differingfrom each other in wavelength, a plurality (N units) of opticalmodulators 126 _(M1) to 126 _(Mn), respectively being disposed at theoutput sides of the respective laser light sources 126 _(L1) to 126_(Ln) to perform switching of the respective output light of laser lightsources, and a single optical multiplexer 126 _(S), which multiplexesthe light transmitted via optical modulators 126 _(M1) to 126 _(Mn),and, by the operation of laser light sources 126 _(L1) to 126 _(Ln) andoptical modulators 126 _(M1) to 126 _(Mn) in accordance with thebranching command signal from the electronic controller 124, outputscontrol light L_(C) of wavelengths λ_(c) that have been selected inaccordance with the routing information (branching information)indicated by the amplitude modulation signals contained in the opticalsignal L_(A11). Semiconductor laser diodes are used, for example, as theplurality of laser light sources 126 _(L1) to 126 _(Ln). In FIG. 20, thecontrol light generator 126 comprises the plurality of laser lightsources 126 _(L1) to 126 _(Ln), which correspond to being the controllight sources that output light, each of a single wavelength anddiffering from each other in wavelength, the single optical multiplexer126 _(S), which multiplexes the light output from the laser lightsources 126 _(L1) to 126 _(Ln) in a single waveguide, and a singleoptical modulator 126 _(M), which is disposed at the output side of theoptical multiplexer 126 _(S) and performs switching of the output lightto cut off the blanking interval, and, by the operation of the laserlight sources 126 _(L1) to 126 _(Ln) and the optical modulator 126 _(M)in accordance with the branching command signal from the electroniccontroller 124, outputs control light L_(C) of wavelengths λ_(c) thathave been selected in accordance with the branching informationcontained in the optical signal L_(A11). In FIG. 21, the control lightgenerator 126 comprises a wavelength variable laser light source 126_(LV), with which the wavelength of the output light can be varied, andthe single optical modulator 126 _(M), which is disposed at the outputside of the wavelength variable laser light source 126 _(LV) andperforms switching of the output light to cut off the blanking interval,and, by the operation of the wavelength variable laser light source 126_(LV) and the optical modulator 126 _(M) in accordance with thebranching command signal from the electronic controller 124, outputscontrol light L_(C) of wavelengths λ_(c) that have been selected inaccordance with the branching information contained in the opticalsignal L₁. For example a distributed Bragg reflection laser, amicromachine surface emission laser, a thermally tuned DFB laser, etc.,is used as the wavelength variable laser light source 126 _(LV). With adistributed Bragg reflection laser, an electric current is injected into a DBR layer (Bragg reflection layer) that makes up one of a pair ofmirrors that make up an optical oscillator of the laser and therefractive index of this portion is varied by a plasma effect to varythe optical oscillation wavelength. With a micromachine surface emissionlaser, the optical oscillation frequency is varied by the variation ofthe optical oscillator length by a micromachine. With a thermally tunedDFB laser, the optical oscillation wavelength is varied by a refractiveindex variation due to temperature. Each of the optical modulators 126_(M1) to 126 _(Mn) and 126 _(M) is arranged, for example, from asemiconductor optical modulator, with which transmitted light isswitched on or off by a drive current or a drive voltage being appliedto a pn junction portion, an externally modulated optical modulator,with which transmitted light is switched on or off by the application ofa drive voltage from the exterior to lithium niobate or othermonocrystal or substance that exhibits an electrooptical effect.

Along with the optical distributor 150, which also functions as thesecond wavelength selector, the optical wavelength converter 118 of FIG.18 makes up an optical signal amplifying triode 128, which is basicallyarranged in the same manner as any of the optical signal amplifyingtriodes 10, 50, 59, 66, 70, 78, and 88 shown in FIG. 1 and FIG. 8 toFIG. 15. As shown in FIG. 22, the present embodiment's opticalwavelength converter 118 has a pair of first optical amplifier 136 andsecond optical amplifier 144, which correspond to being the plurality ofoptical amplifiers that make use of cross gain modulationcharacteristics to amplify, perform wavelength conversion, and outputlight that has been input via first optical fiber 112, equipped inseries and is arranged to amplify the optical signal input via the firstoptical fiber 112 and output the light L₃ of the same wavelength as thecontrol light L_(C) in synchronization with the input of the controllight L_(C) corresponding to the branching information contained in theoptical signal. That is, in FIG. 22, a laser light source 130 isarranged from a single-wavelength semiconductor laser and performscontinuous output at fixed intensity of a laser light (second inputlight) L₂ of a wavelength λ₂ of, for example, 1565 nm that is longerthan the wavelength λ₁ of, for example, 1555 nm, of the optical signalL₁ (first input light). A third optical coupler 132 functions as thefirst optical input means that overlaps (multiplexes) the optical signalL₁, which had been amplitude modulated and transmitted inside the firstoptical fiber 112, with the laser light L₂, which is continuous light,and outputs the multiplexed light to the first optical amplifier 136 viathe first optical circulator 34.

As with the first optical amplifier 26, shown in FIG. 2, each of thefirst optical amplifier 136 and the second optical amplifier 144 isarranged from a semiconductor optical amplifier (SOA). Since the firstoptical amplifier 136 is equipped on one end face thereof with areflecting means 136 d, which is a mirror having an end face treatmentfor reflection of light applied thereto by sputtering, etc., input oflight or output of light is carried out through the other end facepositioned at the opposite side of the one end face. The multiplexedlight of the optical signal L₁ (first input light) and the laser light(second input light) L₂ of the longer wavelength λ₂ is thus input intothe first optical amplifier 136 through the above-mentioned other endface, and light reflected by the reflecting means 136 d is output bypassing through the other end face again. As with the first opticalamplifier 26 shown in FIG. 2, in the active layer of the first opticalamplifier 136, light of the second wavelength λ₂ is amplified upon beingmodulated in the same manner as but inversely in phase with respect tothe modulation of optical signal L₁ and then output from the firstoptical amplifier 136. The first optical amplifier 136, as well as thesecond optical amplifier 144, is thus equipped with cross gainmodulation characteristics, that is, mutual gain modulationcharacteristics.

In FIG. 22, a first optical circulator 134 guides the light output fromthe first optical amplifier 136 not to the third optical coupler 132 butto a first wavelength selector 138. The first wavelength selector 138extracts light of 1565 nm, which is the second wavelength λ₂, from amongthe light output from the first optical amplifier 136. This firstwavelength selector 138 functions as an optical filter element and, forexample, is a fiber grating filter, which is formed by making a portionof an optical fiber vary periodically in refractive index in thelongitudinal direction by localized illumination of ultraviolet rays andselectively transmits light at a half-width, for example, of 1 nm toless than 20 nm with respect to a central wavelength of the secondwavelength λ₂. The first wavelength selector 138 may instead be arrangedfrom either a multilayer film filter, formed by layering a plurality oflayers that differ in refractive index, or a photonic crystal, having aphotonic bandgap.

A fourth optical coupler 140 functions as the second optical input meansthat overlaps (multiplexes) light of the second wavelength λ₂, which hasbeen selected by the first wavelength selector 138 from among the lightoutput from the first optical amplifier 136, and the control lightL_(C), which is laser light of a third wavelength λ₃, and inputs themultiplexed light via a second optical circulator 142 into the secondoptical amplifier 144, which is arranged in the same manner as the firstoptical amplifier 136. At the second optical amplifier 144, the secondwavelength λ₂, which has been modulated in the first optical amplifier136, is subject to further modulation by the control light L_(C) of thethird wavelength λ₃ that is within the wavelength range of spontaneouslyemitted light centered about the second wavelength λ₂, and a mixed lightof the light of the wavelength λ₂ with the modulated light (output lightsignal) L₃, which is made the same in wavelength as the control lightL_(C), is output. The second optical circulator 142 guides this mixedlight (light of the wavelength λ₂ and the modulated light L₃), outputfrom the second optical amplifier 144, not to the fourth optical coupler140, but to an optical distributor 150.

Since the modulated light L₃, which is contained in the light outputfrom the second optical amplifier 144, is light of the third wavelengthλ₃, which is the same as the wavelength of the control light L_(C), whenthe wavelength of the control light L_(C) is varied, for example, toλ_(c1), λ_(c2), λ_(c3), . . . λ_(cN), the wavelength of the light L₃from the second optical amplifier 144 is also varied, for example, toλ_(c1), λ_(c2), λ_(c3), . . . λ_(cN). FIG. 23 shows the waveform of theoutput light L₄ of the optical distributor 150 when the optical signalL₁ (first input light) is experimentally set to the waveform shown inthe top stage of the Figure and the control light L_(C) is set to thewaveform shown in the middle diagram of the Figure. The intensityvariation of the control light L_(C) corresponds to the amplitudemodulation of the output light L₄ of the optical distributor 150 that isshown in the bottom stage, and the output light L₄ of the opticaldistributor 150 has a gain of approximately 2 times to 30 times withrespect to the control light L_(C). Also, the phase of the output lightL₄ is the same as and not inverted with respect to that of the opticalsignal L₁ (first input light).

FIG. 24 shows the characteristics in the case where, in the wavelengthconverter 118 and the optical distributor 150 that function as theoptical signal amplifying triode 128 by being arranged in theabove-described manner, the active layer of the first optical amplifier136 is arranged from quantum dots. In FIG. 24, the frequencycharacteristics of the output light L₄ are shown in a two-dimensionalcoordinate system with the abscissa indicating the frequency of thesignal light L_(A11), which is the first input light, and the ordinateindicating the signal modulation degree H (%) of the output light L₄,which is the output light. As shown in FIG. 24, lowering of the signalmodulation degree H is not seen up to 100 GHz. This signal modulationdegree H is expressed, for example, by the Equation (1) described above.

Returning now to FIG. 18, the modulated light L₃, among the light fromthe above-mentioned wavelength converters 118, are selectivelydistributed by the optical distributors 150, in accordance with theirwavelengths, that is, the wavelengths λ_(c)(=λ_(c1), λ_(c2), λ_(c3), . .. λ_(cN)) of the control light L_(C), among cross-connected fibers F₁₁₁to F_(11M), F₁₂₁ to F_(12M), . . . F_(1N1) to F_(1NM), which have beenset in advance to correspond to a plurality of waveguides. Of the lightfrom each wavelength converter 118, light of the wavelength λ₂, whichdiffers from wavelengths λ_(c), is distributed to a branch optical fiberF_(B0). Since the terminal end of this branch optical fiber F_(B0) isnot connected to a subsequent stage but is closed, the propagation oflight of the wavelength λ₂ is stopped here. Each optical distributor 150thus also functions as the second wavelength selector that selectsoutput light of the third wavelength λ_(c) from the light from thesecond optical amplifier 144.

With the optical distributors 150, when, for example, the modulatedlight L₃ are each a monochromatic light of one wavelength amongwavelengths λ_(c) of the control light L_(C), these are distributedalternatively to one set among the cross-connected fiber sets F₁₁₁ toF_(11M), F₁₂₁ to F_(12M), . . . F_(1N1) to F_(1NM), and in the casewhere the modulated light L₃ are each a mixture of two types, it isdistributed to two sets among the cross-connected fiber sets F₁₁₁ toF_(11M), F₁₂₁ to F_(12M), . . . F_(1N1) to F_(1NM). The opticaldistributors 150 are arranged, for example as shown in FIG. 25, fromarray waveguide grating type optical splitters that are equipped withfirst slab waveguides 150 b, connected to input ports 150 a, second slabwaveguides 150 d, connected to pluralities of output ports 150 c,pluralities of array waveguides 150 e of different lengths, disposedbetween the first slab waveguides 150 b and the second slab waveguides150 d, and the cross-connected fibers F₁₁₁ to F_(11M), F₁₂₁ to F_(12M),. . . F_(1N1) to F_(1NM), respectively connected to the plurality ofoutput ports 150 c, and distribute the modulated light L₃ (input light)from the wavelength converters 118, which are input from the input ports150 a, to output ports among the pluralities of output ports 150 c, thatis, fibers among the cross-connected fibers F₁₁₁ to F_(11M), F₁₂₁ toF_(12M), . . . F_(1N1) to F_(1NM) in accordance with the wavelength ofthe input light. The optical distributors 150 are equipped as necessarywith optical systems, comprising converging lenses for convergingbranched light to the end faces of cross-connected fibers F₁₁₁ toF_(11M), F₁₂₁ to F_(12M), . . . F_(1N1) to F_(1NM). With the presentembodiment, the above-described control light generator 126, wavelengthconverter 118, and optical distributor 150 make up the principalportions of the main optical signal relay unit R_(B1).

FIG. 26 is a diagram showing the conceptual arrangement of the opticalsignal L_(A11) of the wavelength λ₁, which has been transmitted via theinput optical fiber F_(A1) and separated by the splitter S₁, and FIG. 27shows diagrams illustrating a waveform to which the amplitude modulationof the signal light L_(A11) has been added and a process of adding theamplitude modulation. In FIG. 26, the optical signal L_(A11) is a signaltrain that is referred to, for example, as a packet, and at a headportion or front end portion thereof are provided a header portion H, towhich is added such header information as the packet title, date,document name, page number, etc., and a label portion (tag portion)L_(A), to which is added signals indicating such routing information asroute information, data link layer connection information, etc. With theoptical signal L_(A11), the routing information are added to at leastone of either header portion H or label portion L_(A) by the applicationof amplitude modulation as shown in FIG. 27. This amplitude modulationis carried out, for example, by the overlapping of the modulation signalshown in the second stage of FIG. 27 to the main signal shown in the topstage of FIG. 27 using the wavelength converter 118, shown in FIG. 22,or an amplitude modulator, such as that shown in FIG. 30 and which is tobe described later.

FIG. 28 shows time charts illustrating the actions of the first mainrelay unit R_(B11), shown in FIG. 18, as a representative example fordescribing the actions of the present embodiment's optical relay 110that is arranged as described above. In first main relay unit RB₁₁, theoptical signal L_(A11), shown at the top stage of FIG. 28, is input viathe optical delay element 116 into the wavelength converter 118 (inputstep). Meanwhile, a portion of the optical signal L_(A11) is supplied bythe first optical coupler 114 to the electronic controller 124 uponconversion into an electrical signal by the photoelectrical signalconverter 122, the modulation pulse signals (routing information), whichare extracted by the electronic controller 124 and are shown in thesecond stage of FIG. 28, are supplied to the control light generator126, control light L_(C) of wavelengths λ_(c), which have beendetermined in accordance with the routing information indicated by themodulation pulse signals, are generated by the control light generator126 as shown in the third stage of FIG. 28, and in synchronization tothis generation, the optical signal L_(A11) is input into the wavelengthconverter 118 and is output upon being converted to the wavelengthsλ_(c) of the control light L_(c) at the wavelength converter 118(wavelength conversion step). This synchronization is carried out by theoptical signal L_(A11) being delayed by the optical delay element 116 byjust the amount of time corresponding to the operational operation timeof the electronic controller 124 after photoelectric conversion by thephotoelectrical signal converter 122, etc. For example, when the routinginformation indicated by an amplitude modulation pulse P₁ contained inthe optical signal L_(A11) indicates the wavelength bus of thewavelength λ₁, control light L_(C) of the wavelength λ₁ is generated andthe optical signal L_(A11) is converted to the wavelength λ₁ as shown inthe second stage from the bottom of FIG. 28 and output from thewavelength converter 118. Also, when the routing information indicatedby the amplitude modulation pulse P₁ contained in the optical signalL_(A11) indicates the wavelength bus of the wavelength λ₂, control lightL_(C) of the wavelength λ₂ is generated and the optical signal L_(A11)is converted to the wavelength λ₂ as shown in the bottom stage of FIG.28 and output from the wavelength converter 118 and is then distributedaccording to the wavelength by the optical distributor 150 (opticaldistribution step). Here, with the optical signal L_(A11), which is theinput light since a gain by which the output of the first opticalamplifier 136 will saturate is set, the optical signal, which is outputfrom the first optical amplifier 136 and then input via the firstwavelength selector 138 into the second optical amplifier 144, will beof a fixed magnitude, the optical signal after wavelength conversionthat is output from the second optical amplifier 144 and then input intothe optical distributor 150 will be of fixed amplitude, and amplitudemodulation will thus be facilitated. With the wavelength converter 118of the optical relay 110 of the present embodiment, there is no phaseinversion between the signal of the optical signal L_(A11), which is theinput light, and the signal of the output light L₃ or L₄, thus providingthe merit of there being a high degree of freedom in that any wavelengthwithin the gain range of the first optical amplifier 136 may be selectedas the wavelength of the optical signal L_(A11).

FIG. 29 shows time charts illustrating another action of the first mainrelay unit RB₁₁, shown in FIG. 18, as a representative example todescribe another action of the optical relay 110, that is, the action ofperforming wavelength conversion at the same time as labeling and thenoutputting the resulting signal. In first main relay unit RB₁₁, theoptical signal L_(A11), shown at the top stage of FIG. 29, is input viathe optical delay element 116 into the wavelength converter 118.Meanwhile, a portion of the optical signal L_(A11) is supplied by thefirst optical coupler 114 to the electronic controller 124 uponconversion into an electrical signal by the photoelectrical signalconverter 122, the modulation pulse signals (routing information), whichare extracted by the electronic controller 124 and are shown in thesecond stage of FIG. 29, are supplied to the control light generator126. At the control light generator 126, control light L_(C) ofwavelengths λ_(c), which have been determined in accordance with therouting information indicated by the modulation pulse signals, aregenerated, and in synchronization to this generation, the optical signalL_(A11) is input into the wavelength converter 118 and output from thewavelength converter 118 upon conversion to the wavelengths λ_(c) of thecontrol light L_(C). Since the modulation pulse signals here containrouting information to be re-attached, the electronic controller 124makes the control light L_(C) be amplitude modulated and generated so asto contain the pulse signals indicating the routing information as shownin the third stage of FIG. 29. For example, when the routing informationindicated by an amplitude modulation pulse P₁ contained in the opticalsignal L_(A11) indicates the wavelength bus of the wavelength λ₁,control light L_(C) of the wavelength λ₁ is generated and the opticalsignal L_(A11) is converted to the wavelength λ₁ as shown in the secondstage from the bottom of FIG. 29 and output from wavelength converter118. Also, when the routing information indicated by the amplitudemodulation pulse P₁ contained in the optical signal L_(A11) indicatesthe wavelength bus of the wavelength λ₂, control light L_(C) of thewavelength λ₂ is generated and the optical signal L_(A11) is convertedto the wavelength λ₂ as shown in the bottom stage of FIG. 29 and outputfrom the wavelength converter 118.

As described above, with the present embodiment, amplitude modulationsignals are added as routing information to the optical signal trainL_(A11) and the optical signal L_(A11) is transferred to thedestinations indicated by the amplitude modulation signals. Thus in thecase where an amplitude modulated optical signal train is input into thecross gain modulation type wavelength converter 118, when the controllight L_(C) of the wavelength corresponding to the routing informationindicated by the amplitude modulation of the optical signal L_(A11) issupplied to the cross gain modulation type wavelength converter 118,output light of the same wavelengths as the control light L_(C) areoutput and routing is carried out, for example, by the output lightbeing distributed among the transmission paths corresponding to thewavelengths by means of optical distributor 150. A routing device, thatis, the optical signal transfer device or optical signal relay device110 of high speed and compact size can thus be arranged.

Also with the present embodiment, since the amplitude modulation addedto the optical signal train L_(A11) is added at a modulation degree ofno more than 90%, the optical signal L_(A11) is not degraded and yet therouting information is added to the optical signal without fail. Also,since the optical signal train L_(A11) is a packet signal and therouting information are label information or tag information provided ata head portion of the packet signal, the label information or taginformation are added by amplitude modulation to the label portion L_(A)or the tag portion.

Also since the present embodiment includes (a) the input step ofinputting the optical signal train L_(A11), to which amplitudemodulation has been applied as routing information, into the cross gainmodulation type wavelength converter 118, (b) the wavelength conversionstep of supplying the control light L_(C), of wavelengths that differfrom that of the optical signal L_(A11) and correspond to the amplitudemodulation signals, to the above-mentioned cross gain modulation typewavelength converter 118 and making optical signals of the wavelengthsof the control light L_(C) be output from the cross gain modulation typewavelength converter 118, and (c) the optical distribution step ofinputting the optical signals, output from the cross gain modulationtype wavelength converter 118, into the optical distributor 150 anddistributing the optical signals according to their wavelengths amongthe plurality of optical transmission paths connected to the opticaldistributor 150, the optical signal L_(A11) is distributed among theplurality of optical transmission paths connected to the opticaldistributor 150 at the wavelengths that are in accordance with therouting information indicated by the amplitude modulation signals.

Also with the present embodiment, since in the above-mentionedwavelength conversion step, new routing information are re-added to theoptical signal L_(A11), output from the cross gain modulation typewavelength converter 118, by applying amplitude modulation using thecontrol light L_(C) to the optical signal L_(A11) and transferdestinations can thus be re-added as suited inside the optical signalrelay (transfer) device 110, dynamic routing, by which the transferroute is determined, for example, according to the link state, nodestate, and traffic state, is enabled.

Also with the optical signal relay device 110 of the present embodiment,when the optical signal train L_(A11), having amplitude modulationsignals added as routing information, is transmitted, the control lightL_(C) of wavelengths, corresponding to the destinations indicated by theamplitude modulation signals of the optical signal train L_(A11) anddiffering in wavelength from the optical signal L_(A11), are generatedfrom the amplitude modulation signals of the optical signal trainL_(A11) by the control light generator 126, the optical signal trainL_(A11) is converted into optical signals of the wavelengths of thecontrol light L_(C) by the cross gain modulation type wavelengthconverter 118, and the optical signals output from the cross gainmodulation type wavelength converter 118 are distributed among theplurality of optical transmission paths in accordance with theirwavelengths by the optical distributor 150. A routing device, that is,the optical signal transfer device or optical signal relay device 110 ofhigh speed and compact size can thus be realized.

Also since the present embodiment is equipped with the electroniccontroller 124 that makes the control light L_(C) of wavelengths, whichare in accordance with the routing information indicated by theamplitude modulation signals contained in the optical signal L_(A11), begenerated from the control light generator 126 in accordance with theamplitude modulation signals, and the cross gain modulation typewavelength converter 118, having a wavelength conversion function and aswitching function, can thus output optical signals of wavelengthscorresponding to the routing information and these signals can then bedistributed by the optical distributor 150, a routing device, that is,the optical signal transfer device or optical signal relay device 110 ofhigh speed and compact size can be realized.

Also, with this embodiment, since (a) the first optical coupler (opticalsplitter) 114, which branches and thereby supplies optical signalL_(A11), propagating inside the optical fiber 112, to the electroniccontroller 124, (b) the photoelectric converter 122, which converts theoptical signal branched by the first optical coupler 114 into anelectrical signal and supplies the electrical signal to the electroniccontroller 124, and (c) the optical delay element 116, which is disposedat the downstream side of the first optical coupler 114 along theoptical fiber 112 and delays the optical signal L₁ to be input from thefirst optical fiber 112 into the wavelength converter 118, are providedand the electronic controller 124 extracts the amplitude modulationsignals contained in the optical signal L_(A11) and makes the controllight L_(C) of wavelengths corresponding to the routing informationindicated by the amplitude modulation signals be generated from thecontrol light generator 126, the cross gain modulation type wavelengthconverter 118, having a wavelength conversion function and a switchingfunction, can output optical signals of wavelengths corresponding to therouting information and these signals can then be distributed by theoptical distributor 150. A routing device, that is, an optical signaltransfer device or optical signal relay device of high speed and compactsize can thus be realized. Also, since while a portion of the opticalsignal L_(A11) is branched from the first optical coupler 114 andsupplied to the electronic controller 124, the other portion of theoptical signal L_(A11) is delayed by the optical delay element 116 andthen supplied to the wavelength converter 118, despite the delay timeused in the electronic signal processing by the electronic controller124, the control light L_(C), supplied from the control light generator126 to the wavelength converter 118 are favorably synchronized with theoptical signal L₁ at the wavelength converter 118.

Also with the present embodiment, since the cross gain modulation typewavelength converter 118 comprises (a) the first optical amplifier 136and the second optical amplifier 144, each using cross gain modulationcharacteristics to amplify and perform wavelength conversion on inputlight and then outputting the resulting light, (b) the third coupler(first optical multiplexer) 132 that multiplexes the signal lightL_(A11) of the first wavelength λ₁, which is input from the opticalfiber 112, with the laser light (second input light) L₂, which iscontinuous light of the wavelength λ₂ that differs from that of thesignal light L_(A11), and inputs the multiplexed light into the firstoptical amplifier 126, (c) the first wavelength selector 138 thatselects light of the second wavelength λ₂ from among the light from thefirst optical amplifier 136, and (d) the fourth optical coupler (secondmultiplexer) 140 that multiplexes the light of second wavelength λ₂,which has been selected by the first wavelength selector 138, with thecontrol light L_(C) of third wavelength λ₃ and inputs the multiplexedlight into the second optical amplifier 144, and the output light L₃ ofthird wavelength λ₃ is light of the same wavelength as the control lightL_(C) and is modulated in response to the intensity variation of eitheror both of the signal light L₁ of the first wavelength λ₁ and thecontrol light L_(C) of the third wavelength λ₃, and since when light ofsecond wavelength λ₂ that has been selected from the light from thefirst optical amplifier 126, into which the signal light L₁ and thelaser light (second input light) L₂ have been input, and the controllight L_(C) are input into the second optical amplifier 144, themodulated light L₃ or the output light L₄ of the third wavelength λ₃that is selected from the light output from the second optical amplifier144 will thus be light that is modulated in response to the intensityvariation of either or both of the signal light L₁ and the control lightL_(C) and will be an amplified signal with a signal gain of 2 or morewith respect to the control light L_(C), the amplification process ofthe optical signal L₁ can be performed directly using the control lightL_(C).

Also with this embodiment, the optical distributor 150 is equipped withthe first slab waveguide 150 b, connected to the input port 150 a, thesecond slab waveguide 150 d, connected to the plurality of output ports150 c, the plurality of array waveguides 150 e of different lengths,disposed between the first slab waveguide 150 b and the second slabwaveguide 150 d, and the branch optical fibers F_(B1), F_(B2), F_(B3), .. . F_(Bn), respectively connected to the plurality of output ports 150c, and is arranged to distribute the output light L₃ (input light),which are input into the input port 150 a from the wavelength converter118, to output ports among the plurality of output ports 150 c, that is,fibers among the branch optical fibers F_(B1), F_(B2), F_(B3), . . .F_(Bn) in accordance with the wavelengths of the input light. Themodulated light L₃ of the same wavelengths as the control light L_(C),which are output from the wavelength converter 18, are thus favorablydistributed selectively to fibers among optical fibers F_(B1), F_(B2),F_(B3), . . . F_(Bn) in accordance with the wavelengths.

Also, since the present embodiment's optical signal relay device 110 hasa plurality of single-wavelength laser light sources (control lightsources) or a wavelength variable laser light source, outputting controllight of a plurality of priorly set types of wavelengths, and isequipped with the control light generator 126, which supplies thecontrol light L_(C) of the wavelengths selected in accordance with thebranching information contained in the optical signal L₁ to thewavelength converter 118, the optical signal L₁ is selectivelydistributed in accordance with the wavelengths of the control lightL_(C) to certain priorly set optical fibers among the optical fibersF_(B1), F_(B2), F_(B3), . . . F_(Bn) that correspond to the plurality ofbranch optical waveguides.

Also since the present embodiment's control light generating device 126is equipped with the optical modulator 126 _(M) for switching thecontrol light output from the plurality of types of laser light sources126 _(L1) to 126 _(Ln) or wavelength variable laser light source 126_(LV), the control light L_(C) of mutually different wavelengths thatare output from the control light generator 126 are made sharp in theirleading edges and trailing edges and the response characteristics arethus improved.

Also since the present embodiment is equipped with the electroniccontroller 124, which makes the control light generator 126 generate thecontrol light L_(C), having wavelengths that are in accordance with thebranching information contained in the optical signal L₁ input from thefirst optical fiber 112, in accordance with the branching information,the modulated light L₃, output from the wavelength converter 118, isswitched in wavelength in accordance with the routing (branching)information contained in the optical signal L_(A11) and are selectivelydistributed according to the wavelengths to fibers among the pluralityof optical fibers F_(B1), F_(B2), F_(B3), . . . F_(Bn).

Also with the present embodiment, since the electronic controller 124extracts just the routing information (address signals) contained in theoptical signal L_(A11), input from optical fiber 112 and makes thecontrol light L_(C) of wavelengths corresponding to the address signalsbe generated from the control light generator 126 and electromagneticwaves corresponding to signals besides the address signals will thus notbe generated by the signal processing, the merit that theconfidentiality of the optical signals can be secured is provided.

Another embodiment shall now be described. In the following description,portions in common to the above-described embodiment shall be providedwith the same symbols and description thereof shall be omitted.

FIG. 30 shows an embodiment, with which the first main relay unit RB₁₁,shown in FIG. 18 and FIG. 22 described above, is arranged in anall-optical manner. In FIG. 30, a portion of the input optical signalL_(A11), input into the third optical coupler 132 of the wavelengthconverter 118, is branched by an optical coupler (opticalsplitting/multiplexing element or optical multiplexer/opticalmultiplexer) 164, then multiplexed with laser light L, which arecontinuous light of predetermined wavelengths, that is for example,wavelengths among wavelengths λ₁ to λ_(N), by an optical coupler 166,and input into a semiconductor optical amplifier (SOA) 168, equippedwith cross gain modulation characteristics, in other words, mutual gainmodulation characteristics by being arranged in the same manner as thefirst optical amplifier 136 shown in FIG. 22. For the laser light L,which are continuous light, a laser light source 170, which, forexample, is arranged in the same manner as the laser light sources 126_(L1) to 126 _(LN) and the optical multiplexer 126 _(S), shown in FIG.19 and FIG. 20, or the variable laser light source 126 _(LV), shown inFIG. 21, is used. This semiconductor optical amplifier 168 is arrangedto have characteristics such that the response speed is slow relative tothe first semiconductor optical amplifier 136 and the secondsemiconductor optical amplifier 144. For example, in the case where eachof the first semiconductor optical amplifier 136 and the secondsemiconductor optical amplifier 144 is equipped with an active layerarranged from quantum wells or quantum dots as described above, thesemiconductor optical amplifier 168 is arranged with an active layerarranged from bulk. By adjustment and setting of either or both the gainand polarization states, the semiconductor optical amplifier 168 isarranged so as not to respond to high-speed switching. Thus when theinput optical signal L_(A11), shown in the top stage of FIG. 31, isinput, since the control optical signal L_(C) (second stage or thirdstage of FIG. 31) of waveforms corresponding to the amplitude modulationsignals of the input optical signal L_(A11) are input from thesemiconductor optical amplifier 168 into the fourth optical coupler(second optical multiplexer) 140, the output optical signals L₃ of thewavelengths λ₁ or λ_(N), which have been amplitude modulated as shown inthe second stage from the bottom or the bottom stage of FIG. 31, areoutput to the optical distributor 150. The amplitude modulation signalsof the output optical signals L₃ indicate, for example, branchinginformation. In the present embodiment, the optical coupler 164, theoptical coupler 166, the semiconductor optical amplifier (SOA) 168, andthe laser light source 170 make up an all-optical controller 172, whichoutputs the control light L_(C) for providing the wavelengths ofwavelength conversion and adding the routing (branching) information.

With the present embodiment, since the optical signals L_(C), generatedby the optical coupler 164, the optical coupler 166, and thesemiconductor optical amplifier 168, adds, in real time, the samerouting information as those contained in the input optical signalL_(A11) to the head portions of the output light train by amplitudemodulation in the same manner as the control light L_(C) of FIG. 18, themerit that the electronic controller 124 of the above-describedembodiment is made unnecessary and an all-optical arrangement is enabledin regard to such switching operation is provided.

Also with the present embodiment, since the all-optical controller,which makes control light L_(C) of wavelengths that are in accordancewith the routing information indicated by the amplitude modulationsignals contained in the optical signal L_(A11) be generated from thecontrol light generator 126 in accordance with the amplitude modulationsignals, is equipped and control is performed so as to generate controllight of signals that are in accordance with the routing informationindicated by the amplitude modulation signals contained in input opticalsignal L_(A11), and the cross gain modulation type wavelength converter118, having a wavelength conversion function and a switching function,can thus output optical signals of wavelengths corresponding to therouting information and these signals can then be distributed by theoptical distributor, a routing device, that is, an optical signaltransfer device or optical signal relay device of high speed and compactsize can be realized. Since electromagnetic waves are not generated bythe optical signal processing, the merit that the confidentiality of theoptical signals is secured is provided.

FIG. 32 is a diagram, corresponding to FIG. 17, illustrating anall-optical type optical signal relay device 180 that is arranged usingthe art of the above-described wavelength converter 118 of FIG. 30. Thisarrangement shall now be described using the input optical signalL_(A11) of wavelength λ₁, among the plurality of light split by theoptical splitter S₁, as a representative example. As with thearrangement of FIG. 30, a portion of the input optical signal L_(A11),input into the third optical coupler (first optical multiplexer) 132 ofthe wavelength converter 118, is branched by the optical coupler 164,then multiplexed with the laser light L, which are continuous light ofpredetermined wavelengths, that is for example, wavelengths amongwavelengths λ₂ to λ_(N), by the optical coupler 166, and input into thesemiconductor optical amplifier (SOA) 168, equipped with cross gainmodulation characteristics, in other words, mutual gain modulationcharacteristics by being arranged in the same manner as the firstoptical amplifier 136. The present embodiment differs from theembodiment of FIG. 30 in that wavelengths, among the other wavelengthsX₂ to λ_(N) resulting from the splitting of the laser light L, which arecontinuous light, by the optical splitter S₁, are used. Thus when asshown in FIG. 31, the input optical signal L_(A11), shown in the topstage, is input, since the optical signal L_(C) (second stage or thirdstage of FIG. 31) of waveforms corresponding to the amplitude modulationsignals of the input optical signal L_(A11) are input from thesemiconductor optical amplifier 168 into the fourth optical coupler(second optical multiplexer) 140, the output optical signals L₃ ofwavelengths λ₁ or λ_(N), shown in the second stage from the bottom orthe bottom stage of FIG. 31, are output to the optical distributor 150.This embodiment provides the merit of enabling arrangement in a morefully optical manner.

Yet another embodiment shall now be described.

With the above-described embodiments, there is the possibility that inthe relay process of converting an optical packet signal, which is, aninput optical signal L_(ANM), in another main relay unit RB_(MN), to apredetermined wavelength and outputting the result to a predeterminedfiber F_(BNM), an optical signal of the same wavelength may be outputredundantly from the main relay unit RB₁₁, which performs the relayprocess on an optical signal, which is, the input optical signalL_(A11), thereby causing overlapping of optical signals. In such a case,for example the embodiment of FIG. 18 is arranged so that when theelectronic controller 124 detects header information, added by theamplitude modulation signals to the header portion H at the head of theoptical packet signal that is the input optical signal L_(A11), beforethe main relay unit RB_(MN), which is performing a relay processpriorly, confirms the end terminal of the corresponding optical packetsignal, information that instructs diversion is added to the opticalpacket signal by amplitude modulation. For example, though the finaldestination information is not changed, an intermediate address ischanged by amplitude modulation. With this embodiment, when a pluralityof optical packet signals are about to be sent substantiallysimultaneously to a certain fiber F_(BNM) Of the same transmission path,mutual collision of the packet signals can be avoided.

FIG. 33 is a diagram showing the principal parts of a relay device 110,which is arranged so that during the relay process in the other mainrelay unit RB_(MN), wherein an optical packet signal, that is, an inputoptical signal L_(ANM) is converted to a predetermined wavelength andoutput to a predetermined fiber F_(BNM), an optical packet signal, thatis, an input optical signal L_(A11), which has arrived overlappingly intiming, is stored temporarily and the relay process thereof is enabledafter completion of the relay process of the optical packet signal thatis being converted to the above-mentioned predetermined wavelength. InFIG. 33, a plurality of optical signal storage elements 174, formed byconnecting in parallel a plurality of optical fibers that differ inlength in order to temporarily store optical packet signals distributedby the optical distributor 150, an optical feedback transmission path,that is, a feedback optical fiber 178, feeding back optical signaloutput from the optical signal storage elements 174 to the input side,and an optical coupler 176, re-inputting an optical packet signal of anyof standby wavelengths λ₀₁ to λ₀₃, which has been transmitted to theinput side via the feedback optical fiber 178, as the input opticalsignal L_(A11) into the first coupler 114, are equipped. When during arelay process in the other main relay unit RB_(MN), wherein an opticalpacket signal, that is, the input optical signal L_(ANM) is converted toa predetermined wavelength and output to a predetermined fiber F_(BNM),it is judged that an optical packet signal L_(A11), which has routinginformation and which the main relay unit RB₁₁ is to output to thepredetermined fiber F_(BNM) in accordance with the header informationattached by amplitude modulation signals to the header portion H at thehead of the optical packet signal, is received, the electroniccontroller 124 judges that this optical packet signal L_(A11) is to bestored temporarily. In response to a signal from the electroniccontroller of the other main relay unit RB_(MN), the electroniccontroller 124 makes the control light generator 126 output a controlsignal among control signals L_(C01) to L_(C03) for conversion of theoptical pack signal L_(A11) to a wavelength among the priorly setstandby wavelengths λ₀₁ to λ₀₃. The optical signal of a wavelength amongthe standby (temporary storage) wavelengths λ₀₁ to λ₀₃ that is outputfrom the optical distributor 150 is sent to one of the optical signalstorage elements 174 connected to the optical distributor 150 and, afterbeing stored there for a predetermined amount of time, is transmittedvia the feedback optical fiber 178 to the optical coupler 176 and thenre-input as the input optical signal L_(A11) into the first coupler 114and subject again to the above-described relay process. The plurality ofoptical signal storage elements 174 are respectively arranged, forexample, like the above-described optical delay element 116 and, inorder to be equipped with lengths corresponding to storage time requiredby the optical packet signals to be stored therein, are respectivelyarranged by winding a plurality of optical fibers of mutually differentoptical lengths that are required for propagation for just thecorresponding storage time. With the present embodiment, mutualcollision of a plurality of optical packet signals that are about to besent substantially simultaneously to the same transmission path, thatis, a predetermined fiber F_(BNM) can be prevented.

Also with the above-described embodiment of FIG. 18, the electroniccontroller 124 may be arranged to generate the control light L_(C) thatmake wavelength converter 118 execute wavelength conversion processesselectively so that, for example, for input optical signals L_(A11) toL_(A1N), L_(A21) to L_(A2N), . . . L_(AM1) to L_(AMN), the processingtime zones are mutually differed according to the wavelength set ortransmission path set in order to transfer the desired wavelengths tothe desired transmission paths.

Also with the wavelength converter 118, though the third optical coupler132, the fourth optical coupler 140, the first optical amplifier 136,the second optical amplifier 144, the first wavelength selector 138 andother component parts may be connected by optical fibers these mayinstead be coupled by means of optical waveguides, etc., formed on asemiconductor substrate or a substrate formed of a light transmittingsubstance, such as a glass substrate.

Though the optical distributor 150 is equipped with the first slabwaveguide 150 b, connected to the input port 150 a, the second slabwaveguide 150 d, connected to the plurality of output ports 150 c, theplurality of array waveguides 150 e of different lengths, disposedbetween the first slab waveguide 150 b and the second slab waveguide 150d, and the branch optical fibers F_(B1), F_(B2), F_(B3), . . . F_(Bn),respectively connected to the plurality of output ports 150 c, and isarranged to distribute the output light L₃ (input light), input into theinput port 150 a from the wavelength converter 118, to output portsamong the plurality of output ports 150 c, that is, fibers among thebranch optical fibers F_(B1), F_(B2), F_(B3), . . . F_(Bn) in accordancewith the wavelength of the input light, the optical distributor 150 mayinstead be arranged from a diffraction grating type opticalmultiplexer/splitter that makes use of the diffraction angles of adiffraction grating that differ according to wavelength to selectivelydistribute the output light L₃, which is the light that is inputthereinto, among the plurality of branch optical fibers F_(B1), F_(B2),F_(B3), . . . F_(Bn) that are aligned in array form, or be arranged froma prism optical multiplexer/splitter that uses a prism in place of thediffraction grating. In this case, the optical distributor 150 isarranged from a prism type optical distributor that makes use of therefraction angles of a prism that differ according to wavelength toselectively distribute the input light among the plurality of arraywaveguides aligned in array form. The same applies to the opticalsplitters S₁ to S_(M) and the multiplexers T₁ to T_(M).

Also in place of the electronic controller 124 of the above-describedembodiments, an optical operational controller, arranged from anoperational device, comprising a plurality of optical triodes, a laserlight source, etc., may be used. By the use of an all-optical device inplace of the electronic controller 124, the entirety of the opticalsignal relay device 110 becomes arranged from optical elements.

Also, in place of the first optical fiber 112, the second optical fiber120, etc., which are used as the optical waveguides in theabove-described embodiments, two-dimensional optical waveguides, whichguide light in two-dimensional directions, and three-dimensional opticalwaveguides, which guide light in three-dimensional directions, may bedisposed and used at portions of optical circuits.

Also with the above-described embodiments, the optical modulators 126_(M1) to 126 _(Mn) and 126 _(M) may be eliminated from the control lightgenerator 126 shown in FIG. 19, FIG. 20, and FIG. 21. In this case, forexample, with the optical modulator 126 of FIG. 19 and FIG. 20, thecontrol light L_(C) of different wavelengths are output selectively byselective on/off drive of the laser light sources 126 _(L1) to 126_(Ln). Also with the optical modulator 126 of FIG. 21, the control lightL_(C) of different wavelengths are output selectively by stepwisevariation of the injection current into the DBR layer of the wavelengthvariable laser light source 126 _(LV).

FIG. 34 to FIG. 38 illustrate examples where an optical signal storagedevice, enabling the taking out of optical signals at desired timings,is applied to an optical multiplexer/splitter for optical communicationfor advanced information processing.

FIG. 34 is a diagram illustrating the arrangement of the principal partsof an optical signal storage device 210. In FIG. 34, a first coupler214, functioning as an optical splitter/multiplexer, an optical delayelement 216, and a cross gain modulation type wavelength converter(optical switching device, main optical signal amplifying triode unit)218 are successively connected to an optical fiber 212 that transmits anoptical packet signal, optical data communication signal or otheroptical signal L_(A) from an optical network, etc.

The optical delay element 216 delays the optical signal transmittedinside the optical fiber 212 for just a predetermined amount of time andis arranged, for example, by winding an optical fiber of predeterminedlength and thereby providing a propagation distance to delay the opticalsignal by the propagation time it takes for the optical signal topropagate across the predetermined propagation distance. The delay timeof the optical delay element 216 is determined by experiment in advanceso that the optical signal to be amplified inside the wavelengthconverter 218 will be synchronized with the control light that indicatesthe transmission destination of the optical signal by wavelength.

The branched optical signal, which is branched from the optical signalinside the optical fiber 212 by the first optical coupler 214, issupplied to an electronic controller 224, via an optical fiber 220 and aphotoelectrical signal converter 222 connected thereto. The electroniccontroller 224 is, for example, arranged from a so-called microcomputer,wherein a CPU processes the input signal in accordance with a programstored in advance in a ROM and using the temporary storage function of aRAM. Based on a code signal, that is, routing information indicated byamplitude modulation and contained in the optical signal transmitted viathe optical fiber 220, the electronic controller 224 supplies awavelength command signal, corresponding to the routing information forrouting the optical signal, to a control light generator 126. Theelectronic controller 224 extracts, for example, routing informationcontained in the optical signal L_(A) input from the optical fiber 220and makes control light L_(C), which are in accordance with thewavelengths corresponding to the routing information, be generated fromthe control light generator 226.

The control light generator 226 has a control light source that outputsthe control light L_(C) of a plurality of priorly set types ofwavelengths λ_(c) and, in accordance with the command signal from theelectronic controller 224, that is, in accordance with the wavelengthcommand signal selected in accordance with the branching informationcontained in the optical signal L₁, supplies the control light L_(C) ofwavelengths λ_(c) that correspond to the branching information to thewavelength converter 218. The control light generator 226 generates inan alternative or selective manner, control light L_(C) of a pluralityof types, for example, N types of wavelengths λ₁, λ₂, λ₃, . . . λ_(N) incorrespondence to transfer destination output optical fibers F₁ toF_(N). The FIG. 19, FIG. 20, and FIG. 21 of the above-describedembodiments respectively illustrate arrangement examples of the controllight generator 226. The optical fiber 212, the first optical coupler214, the optical delay element 216, the wavelength converter 218, theoptical fiber 220, the photoelectrical signal converter 222, theelectronic controller 224, the control light generator 226, and theoptical signal distributor 250 of the present embodiment are arranged inthe same manner as the optical fiber 112, the first optical coupler 114,the optical delay element 116, the wavelength converter 118, the opticalfiber 120, the photoelectrical signal converter 122, the electroniccontroller 124, the control light generator 126, and the optical signaldistributor 150 of the above-described embodiments, and the wavelengthconverter 218 and the optical signal distributor 250 make up an opticalsignal amplifying triode 228 of the same arrangement as the opticalsignal amplifying triode 128.

Returning now to FIG. 34, output light L₃ from the wavelength converter218 are selectively distributed by the optical distributor 250 inaccordance with their wavelength, that is, in accordance with thewavelengths λ₁, λ₂, λ₃, . . . λ_(N) of the control light L_(C) tocross-connected fibers F₁, F₂, F₃, . . . F_(N), which have been set inadvance to correspond to a plurality of waveguides. Also, light of thesame wavelength λ_(b) as bias light L₂, which differs from the abovewavelengths, is distributed to a branch optical fiber F_(b). When, forexample, the output light L₃ is a monochromatic light, it is distributedalternatively to one fiber among the cross-connected fibers F₁, F₂, F₃,. . . F_(N), and in the case where output light L₃ are a mixture of twotypes, it is distributed to two sets among the cross-connected fibersF₁, F₂, F₃, . . . F_(N). The cross-connected fibers F₁ and F₂ areconnected to an optical adding circuit 252 for performing a multiplexingprocess on the optical signal L_(A) and an optical dropping circuit 254for performing a splitting process on the optical signal L_(A), and thecross-connected fibers F₃ to F_(N) are connected to optical buffermemory elements M₃ to M_(N). These optical buffer memory elements M₃ toM_(N) are delay elements, each of which is arranged, for example, bywinding an optical fiber of predetermined length and outputs the opticalsignal L_(A) upon delaying the signal by a delay time corresponding tothe time of propagation inside the optical fiber of predeterminedlength.

The optical signal L_(A), which is output from any of theabove-mentioned optical buffer memory elements M₃ to M_(N), is fed back,via a feedback optical fiber 256, which makes up an optical feedbacktransmission path, and a fifth optical coupler (optical multiplexer)258, which is arranged in the same manner as the first optical coupler214, to the optical fiber 212 at the upstream side of the first opticalcoupler 214 and is thereby circulated along a circulation path formed ofthe first optical coupler 214, the optical delay element 216, thewavelength converter 218, the optical distributor 250, one of theoptical buffer memory elements M₃ to M_(N), the feedback optical fiber256, and the fifth optical coupler 258.

With the optical signal storage device 210, arranged as described above,the optical signal L_(A), which is transmitted from the optical fiber212, has the routing signals (labeling) contained therein extracted bythe electronic controller 224 and so that it will be distributed to thetransmission destinations indicated by the routing signals, theelectronic controller 224 controls the control light generator 226 tooutput the control light L_(C) of wavelengths corresponding to therouting signals. When the wavelength of the control light L_(C) is λ₁,since the output light L₃, which is output from the wavelength converter218, will be the optical signal L_(A) of the wavelength λ₁, it isdistributed by optical distributor 250 to the optical adding circuit 252and thus multiplexed or branched. When the wavelength of the controllight L_(C) is λ₂, since the output light L₃, which is output from thewavelength converter 218, will be the optical signal L_(A) of thewavelength λ₂, it is distributed by the optical distributor 250 to theoptical dropping circuit 254 and thus multiplexed or branched.

However, in the case where it is unsuitable to transmit the opticalsignal L_(A) immediately to the optical adding circuit 252 or theoptical dropping circuit 254, the optical signal L_(A) is taken out, byelectronic processing by the electronic controller 224, after thereceiving of a reading timing signal R from the exterior or afterstorage until the elapse of a storage time contained in the opticalsignal L_(A). That is, if the wavelength of the control light L_(C) thatis output from the control light generator 226 to wavelength converter218 is any of λ₃ to λ_(N), that is, if for example this wavelength isλ₃, since the wavelength of the output light L₃ (optical signal L_(A)),output from the wavelength converter 218, will be λ₃, the light will bedistributed by the optical distributor 250 to the optical buffer memoryM₃. After being stored for a fixed amount of time in the optical buffermemory M₃, this optical signal L_(A) is stored by being circulatedrepeatedly along the circulation path formed of the feedback opticalfiber 256, the fifth optical coupler 258, the first optical coupler 214,the optical delay element 216, the wavelength converter 218, the opticaldistributor 250, and the optical buffer memory element M₃. When thisoptical signal L_(A) that is in circulation passes through thewavelength converter 218, the wavelength of the control light L_(C) thatis output from the control light generator 226 to the wavelengthconverter 218 is made λ₃. When during the storage of such an opticalsignal L_(A), another optical signal is input and is to be stored, it isconverted in the same manner as described above to a wavelength thatdiffers from the wavelength λ₃, that is for example to λ₄ and, in thesame manner as described above, is stored by being circulated repeatedlyalong the circulation path formed of the feedback optical fiber 256, thefifth optical coupler 258, the first optical coupler 214, the opticaldelay element 216, the wavelength converter 218, the optical distributor250, and the optical buffer memory element M₄.

And when, for example, the takeout timing signal R for takeout to theoptical adding circuit 252 is supplied to the electronic controller 224from the exterior, the electronic controller 224 makes the control lightgenerator 226 generate the control light L_(C) of the wavelength λ₁ inorder to convert the optical signal L_(A), which is circulatedrepeatedly along the circulation path formed of the feedback opticalfiber 256, the fifth optical coupler 258, the first optical coupler 214,the optical delay element 216, the wavelength converter 218, the opticaldistributor 250, and the optical buffer memory element M₃, to the outputwavelength λ₁ at the cross gain modulation type wavelength converter218. As a result, the optical signal L_(A) is distributed towards theoptical adding circuit 252 by the optical distributor 250 and is thusoutput to the optical adding circuit 252. The electronic controller 224thus also functions as an optical signal storage control means.

With the optical signal storage device 210 of the present embodiment,since the electronic controller 224, which functions as the opticalsignal storage control means, makes the control light generator 226generate the control light L_(C) of the wavelength λl in order toconvert the optical signal L_(A), which is circulated repeatedly alongthe circulation path formed of the feedback optical fiber 256, the fifthoptical coupler 258, the first optical coupler 214, the optical delayelement 216, the wavelength converter 218, the optical distributor 250,and the optical buffer memory element M₃, to the output wavelength λ₁ atthe cross gain modulation type wavelength converter 218, this opticalsignal L_(A) is stored for an arbitrary amount of time and the opticalsignal L_(A) is taken out an arbitrary timing (takeout time) in responseto the output timing indicated by the stored signal output information(reading timing signal R) that is supplied from the exterior or iscontained in the optical signal L_(A).

Also with the present embodiment, since the electronic controller 224,which functions as the optical signal storage control means, makes thecontrol light generator 226 generate the control light L_(C) forconversion of the wavelength of the optical signal L_(A), which is to beinput into the cross gain modulation type wavelength converter 218, to awavelength among the recording wavelengths λ₃ to λ_(N), the storage ofthe optical signal L_(A) is started by the input optical signal L_(A)being converted in wavelength to a wavelength among the recordingwavelengths X₃ to λ_(N) and thereby being circulated in the circulationtransmission path that repeatedly passes through the cross gainmodulation type wavelength converter 218, the optical distributor 250,one of the optical buffer memory elements M₃ to M_(N), the opticalfeedback transmission path 256, the fifth optical coupler 258, the firstoptical coupler 214, and the optical delay element 216.

Also, with this embodiment, since (a) the first optical coupler (opticalsplitter) 214, which branches and thereby supplies the optical signalL_(A), propagating inside the optical fiber 212, to the electroniccontroller 224, (b) the photoelectric converter 222, which converts theoptical signal branched by the first optical coupler 214 into anelectrical signal and supplies the electrical signal to the electroniccontroller 224, and (c) the optical delay element 216, which is disposedat the downstream side of the first optical coupler 214 along theoptical fiber 212 and delays the optical signal L_(A) to be input fromthe first optical fiber 212 into the cross gain modulation typewavelength converter 218 are provided, the electronic controller 224makes the control light generator 226 generate the control light L_(C)of wavelengths corresponding to the routing information contained in theoptical signal L_(A), and the cross gain modulation type wavelengthconverter 218, having a wavelength conversion function and a switchingfunction, can thus output optical signals of wavelengths correspondingto the routing information and these signals can then be distributed bythe optical distributor 250, a routing device, that is, an opticalsignal transfer device or optical signal relay device of high speed andcompact size can be realized. Also, since while a portion of the opticalsignal L_(A) is branched from the first optical coupler 214 and suppliedto the electronic controller 224, the other portion of the opticalsignal L_(A) is delayed by the optical delay element 218 and thensupplied to the wavelength converter 216, despite the delay time used inthe electronic signal processing by the electronic controller 224, thecontrol light L_(C), supplied from the control light generator 226 tothe wavelength converter 218, are favorably synchronized with theoptical signal L_(A) at the wavelength converter 218.

Also with the present embodiment, since the cross gain modulation typewavelength converter 218 comprises (a) the first optical amplifier 236and the second optical amplifier 244, each using cross gain modulationcharacteristics to amplify and perform wavelength conversion on inputlight and then outputting the resulting light, (b) the third coupler(first optical multiplexer) 232 that multiplexes the signal light L_(A)of the first wavelength λ₁, which is input from the optical fiber 212,with the laser light (second input light, bias light) L₂, which iscontinuous light of the wavelength λ₂ that differs from that of thesignal light L_(A), and inputs the multiplexed light into the firstoptical amplifier 136, (c) the first wavelength selector 238 thatselects light of the second wavelength λ₂ from among the light from thefirst optical amplifier 236, and (d) the fourth optical coupler (secondmultiplexer) 240 that multiplexes the light of the second wavelength λ₂,which has been selected by the first wavelength selector 238, with thecontrol light L_(C) of the third wavelength λ₃ and inputs themultiplexed light into the second optical amplifier 244, and the outputlight L₃ of the third wavelength λ₃ is light of the same wavelength asthe control light L_(C) and is modulated in response to the intensityvariation of either or both of the signal light L₁ of the firstwavelength λ₁ and the control light L_(C) of the third wavelength λ₃,and since when the light of the second wavelength λ₂ that has beenselected from the light from the first optical amplifier 236, into whichthe signal light L_(A) and the laser light (second input light) L₂ havebeen input, and the control light L_(C) are input into the secondoptical amplifier 244, the modulated light L₃ or the output light L₄ ofthe third wavelength λ₃ that is selected from the light output from thesecond optical amplifier 244 will thus be light that has been modulatedin response to the intensity variation of either or both of the signallight L₁ and the control light L_(C) and will be an amplified signalwith a signal gain of 2 or more with respect to the control light L_(C),the amplification process of the optical signal L₁ can be performeddirectly using the control light L_(C).

Another embodiment of the optical signal storage device 210 shall now bedescribed.

In order to restrain increase or decrease of the gain of the opticalsignal L_(A), which is stored by being circulated in the circulationtransmission path that repeatedly passes through the cross gainmodulation type wavelength converter 218, the optical distributor 250,one of the optical buffer memory elements M₃ to M_(N), the opticalfeedback transmission path 256, the fifth optical coupler 258, the firstoptical coupler 214, and the optical delay element 216, the electroniccontroller 224 may further comprise an optical signal gain controllingmeans that controls the circulated signal light L_(A) or the controllight L_(C), which is supplied to the cross gain modulation typewavelength converter 218. That is, the electronic controller 224controls the control light L_(C) in accordance with a priorly storedprogram so as to make fixed the gain of the circulated signal lightL_(A), which is input via the first optical coupler 214 and thephotoelectrical signal converter 222. For example, when the gain of thesignal light L_(A) drops, the gain of the control light L_(C) isincreased so that the signal light L_(A) will be amplified at the crossgain modulation type wavelength converter 218, and when the gain of thesignal light L_(A) increases, the gain of the control light L_(C) isdecreased so that the signal light L_(A) will be reduced at the crossgain modulation type wavelength converter 218.

FIG. 35 shows an optical signal storage device 270 of yet anotherembodiment. The optical signal storage device 270 of this embodimentdiffers from optical signal storage device 210 of the above-describedembodiment in that a feedback optical amplifier 272, for restrainingintensity fluctuations, such as oscillatory increase or attenuation,that accompany the storage time (number of times of circulation) of thecirculated optical signal L_(A), is interposed in the feedback opticalfiber 256 and that, of the above-mentioned functions, the electroniccontroller 224 is not provided with the optical signal gain controlfunction of controlling the control light L_(C), supplied to the crossgain modulation type wavelength converter 218 to make fixed the gain ofthe optical signal L_(C), which is stored by being circulated, and isotherwise arranged in the same manner. Also with the present embodiment,the response times (response characteristics) of a first gain controloptical amplifier 276 and a second gain control optical amplifier 280are set to be longer (slower) than those of the first optical amplifier236 and the second optical amplifier 244. For example, either or each ofthe first gain control optical amplifier 276 and the second gain controloptical amplifier 280 is arranged from an optical amplifier, which isslow in the response time of cross gain modulation, such as an opticalamplifier, with which a three-level or four-level energy level system isformed inside a light transmitting medium, for example, by the doping ofelemental erbium or other rare earth element inside an optical fiber oroptical waveguide. By arranging with optical amplifiers of slow responsetimes, the signal components of the circulated optical signal L_(A) aresmoothed and variation of the signal gains thereof are detected readily.

The feedback optical amplifier 272 corresponds to being the optical gaincontrol means and amplifies the optical signal L_(A), which is fed backto the feedback optical fiber 256, based on decrease of the gain of thelight of the same wavelength λ_(b) as the bias light L₂, contained inthe output light from the second optical amplifier 244 of the wavelengthconverter 218. That is, the feedback optical amplifier 272 is equippedwith a laser light source 274, outputting a fixed laser light ofwavelength λ_(p), the first gain control optical amplifier 276,receiving light, which is output via the fiber F_(b) from the opticaldistributor 250 and is of the same wavelength λ_(b) as the bias lightL₂, and the laser light of the wavelength λ_(p) and outputting a gaincontrol light L₅ of the wavelength λ_(p) that decreases in gain inaccompaniment with an increase in gain of the light of the samewavelength λ_(b) as the bias light L₂, a filter 278, transmitting lightof the wavelength λ_(p) from among the output light from the first gaincontrol optical amplifier 276, a second gain control optical amplifier280, receiving the light of the wavelength λ_(p) that has beentransmitted through the filter 278 and the optical signal L_(A), whichis fed back, and outputting the optical signal L_(A) that increases ingain in accompaniment with a decrease in gain of the gain control lightL₅, and a filter 282, transmitting the optical signal L_(A) of anywavelength among the wavelengths λ₃ to λ_(N) from among the output lightfrom the second gain control optical amplifier 280 or not transmittingjust light of the wavelength L₅. By the gain of the fed-back opticalsignal L_(A) being increased or decreased by the second gain controloptical amplifier 280 in accordance with a decrease or increase of thegain of the light of the same wavelength λ_(b) as the bias light L₂ thatis opposite the increase or decrease of the gain of the circulatedoptical signal L_(A), the optical signal L_(A) is restrained fromincreasing and decreasing in gain at each circulation and is thusmaintained at a substantially fixed gain. Also with the presentembodiment, since in addition to the same effects as the above-describedembodiment, the effect that slow attenuation variations are restrainedwhile fast response signals are kept as they are is provided, the meritthat the optical signal L_(A), which is circulated for storage, isrestrained in the increase and decrease of gain and is maintained at asubstantially fixed gain is provided.

FIG. 36 shows time charts that illustrate the actions of the opticalsignal storage device 270. When the optical signal L_(A) is the signalto be stored, the optical signal L_(A) that is input is converted inaccordance with the control light L_(C) (λ₃) to the storage wavelength,such as λ₃, at the wavelength converter 218, then distributed by theoptical distributor 250 to the optical buffer memory M₃. The opticalsignal L_(A) is thereafter circulated along the circulation path formedof the optical buffer memory M₃, the feedback optical fiber 256, thefeedback optical amplifier 272, the feedback optical fiber 256, thefifth optical coupler 258, the wavelength converter 218, and the opticaldistributor 250. In this process, since the gain of the circulatedoptical signal L_(A) is restrained from becoming attenuated and is heldat a fixed level by the feedback optical amplifier 272, if the opticalsignal L_(A) that is input is as shown in the top stage of FIG. 36, theoptical signal L_(A) that is circulated will be in the state shown inthe stage below the top stage. In the case where the optical signalL_(A), which is stored by such circulation, is to be taken out, just anarbitrary interval is converted at an arbitrary timing in accordancewith the control light L_(C) (λ₁) to the output wavelength, which forexample is λ₁, at the wavelength converter 218 and is then output by theoptical distributor 250 to the optical adding circuit 252. The waveformshown at the third stage from the bottom of FIG. 36 is the outputwaveform of this optical signal L_(A). The second stage from the bottomof FIG. 36 shows the other output waveform that remains after theabove-mentioned output.

FIG. 37 shows the signal waveform in the case where the feedback opticalamplifier 272 is not provided and the attenuation of the gain of thecirculated optical signal L_(A) is not restrained. This is the signalwaveform, for example, in the case where the feedback optical amplifier272 is not equipped in the optical signal storage device 270 or in thecase where an optical signal gain control means is not equipped in theelectronic control device 224 of the optical signal storage device 210of FIG. 34. The top and bottom stages of this FIG. 37 correspond to thetop stage and the stage below the top stage of FIG. 36.

FIG. 38 shows an optical signal storage device 290 of another embodimentof this invention. This embodiment's optical signal storage device 290differs from the optical signal storage device 210 of theabove-described embodiment in that the optical delay element 216 and thefirst optical coupler 214 are omitted, an all-optical operationalcontroller 292 is provided in place of the electronic controller 224, anoptical coupler 294 of the same arrangement as the first optical coupler214 is provided in order to branch a portion of optical signal L_(A)that is fed back by the feedback optical fiber 256 and input thisportion into the all-optical operational controller 292, and theall-optical operational controller 292 functions as the optical signalgain control means that restrains the attenuation that accompanies thestorage time (number of times of circulation) of the circulated opticalsignal L_(A) based on the attenuation, and is otherwise arranged in thesame manner.

The all-optical operational controller 292 is equipped, for example,with N sets of optical control circuits, each comprising a laser lightsource, outputting continuous light of wavelength λ₃, an opticalcoupler, multiplexing the laser light of wavelength λ₃ with the readingtiming signal R from the exterior, and a wavelength converter of thesame arrangement as the cross gain modulation type wavelength converter18 that receives the light multiplexed by the optical coupler andoutputs the control light L_(C) of wavelength λ₃ for just the readinginterval of the reading timing signal R, and is thereby arranged to takeout the optical signal L_(A), which is stored by circulation, inresponse to the reading timing signal R that is supplied at an arbitrarytiming. Also, the all-optical operational controller 292 is equippedwith a low-response optical delay element, which receives thecirculating optical signal L_(A), supplied from the optical coupler 294,and forms an envelop curve that indicates the attenuation of the gain ofthe optical signal, and is arranged to supply the light indicating theattenuation curve of the wavelength λ₃ that is output from the opticaldelay element as the control light L_(C) to the cross gain modulationtype wavelength converter 218. Attenuation due to circulation of theoptical signal L_(A) of the wavelength λ₃, which is output from thecross gain modulation type wavelength converter 218, is therebyrestrained. The present embodiment provides the same effects as theembodiment of FIG. 35.

Also, the optical distributor 250 may be an interference film typeoptical distributor. A multilayer filter that is classified as aninterference film is arranged so as to reflect a specific wavelength bylayering several dozen layers of an SiO₂ thin film and a TiO₂ thin filmin alternating manner.

Also, in place of the electronic controller 224 of the above-describedembodiments, an optical operational controller, arranged from anoperational device, comprising a plurality of optical triodes, a laserlight source, etc., may be used. By the use of an all-optical device inplace of the electronic controller 224, the entirety of the opticalsignal storage device 210 becomes arranged from optical elements.

Also with the optical signal storage device 210 of the above-describedembodiment, the numbers of the optical adding circuit 252, the opticaldropping circuit 254, the optical buffer memories M₃ to M_(N) may bechanged variously and portions of these may be eliminated or added.

Also, for example with the cross gain modulation type wavelengthconverter 218, the wavelength λ_(c) of the control light L_(C) may bemade the same as the wavelength λ₁ of the signal light L_(A). In thiscase, the wavelength of the output light L₃ from the cross gainmodulation type wavelength converter 18 will be the same as thewavelength λ₁ of the signal light L_(A).

The above-described embodiments are simply examples of the presentinvention, and various modifications may be applied within a scope thatdoes not fall outside the gist of the present inventions.

1. An optical signal amplifying triode comprising: a first semiconductoroptical amplifier and a second semiconductor optical amplifier, eachequipping an active layer formed of a pn junction and amplifying,performing wavelength conversion on, and then outputting an opticalsignal input therein; a first optical input means, inputting a firstinput light of a first wavelength and a second input light of a secondwavelength into the first semiconductor optical amplifier; a firstwavelength selector, selecting light of the second wavelength from amongthe light from the first semiconductor optical amplifier; a secondoptical input means, inputting the light of second wavelength that hasbeen selected by the first wavelength selector and a third input lightof a third wavelength into the second semiconductor optical amplifier;and a second wavelength selector, selecting output light of the thirdwavelength from among the light from the second semiconductor opticalamplifier; and being characterized in that the output light of the thirdwavelength is modulated in response to the intensity variation of eitheror both of the first input light of the first wavelength and the thirdinput light of the third wavelength and the signal gain with respect tothe third input light of the third wavelength is 2 or more.
 2. Theoptical signal amplifying triode according to claim 1, wherein the firstinput light of the first wavelength is modulated light, the second inputlight of the second wavelength is continuous light, the third inputlight of the third wavelength is control light, and the output light ofthe third wavelength has a signal waveform, with which the modulationsignal of the first input light is amplified, in the input interval ofthe control light.
 3. The optical signal amplifying triode claim 1,wherein the third wavelength is the same as the first wavelength.
 4. Theoptical signal amplifying triode according to claim 1, wherein thesignal gain of the output light of the third wavelength with respect tothe control light of the third wavelength is 10 or more.
 5. The opticalsignal amplifying triode according to claim 1 wherein the active layersof the semiconductor optical amplifiers are arranged from quantum wells,a strained-layer superlattice, or quantum dots.
 6. The optical signalamplifying triode according to claim 1, further comprising: a reflectingmeans, reflecting light that has been transmitted through the activelayer of an above-mentioned semiconductor optical amplifier towards thesemiconductor optical amplifier or the other semiconductor opticalamplifier.
 7. The optical signal amplifying triode according to claim 1,wherein either or each of the first semiconductor optical amplifier andsecond semiconductor optical amplifier is equipped at one face thereofwith a reflecting means that selectively reflects light, and thereflection means is optically coupled via a lens to either or each ofthe first semiconductor optical amplifier and second semiconductoroptical amplifier.
 8. The optical signal amplifying triode according toclaim 6, wherein the reflecting means comprises: a first wavelengthselective mirror, which, among the light from the first semiconductoroptical amplifier, does not reflect the first input light of the firstwavelength but reflects light of the second wavelength to the secondsemiconductor optical amplifier; and a second wavelength selectivemirror, which, among the light from the second semiconductor opticalamplifier, does not reflect the second input light of the firstwavelength but reflects light of the third wavelength.
 9. The opticalsignal amplifying triode according to claim 6, wherein a wavelengthselective filter, which does not transmit light of the first wavelengthbut transmits light of the second wavelength, is disposed between oneend face of the first semiconductor optical amplifier and the reflectingmeans for reflecting light, and a wavelength selective filter, whichdoes not transmit light of the second wavelength but transmits thewavelength of the control light, is disposed between one end face of thesecond semiconductor optical amplifier and the reflecting means forreflecting light.
 10. The optical signal amplifying triode according toclaim 6, wherein the reflecting means functions as either or both of thefirst wavelength selector and second wavelength selector and the outputlight from an above-mentioned semiconductor optical amplifier is inputinto the other semiconductor optical amplifier by changing one or bothof the incidence angle of the input light and the emission angle of theoutput light with respect to the reflecting means.
 11. The opticalsignal amplifying triode according to claim 1, wherein a plurality ofsets of the first semiconductor optical amplifier and secondsemiconductor optical amplifier are disposed in optical waveguidesformed on a semiconductor substrate and these sets are integrated as asingle chip.
 12. The optical signal amplifying triode according to claim1, further comprising an optical circulator or a directional coupler,which makes input light be input into an above-mentioned semiconductoroptical amplifier through one end face of the semiconductor opticalamplifier and guides light, output from the semiconductor opticalamplifier through the one end face, to an optical path that differs fromthat of the input light.
 13. The optical signal amplifying triodeaccording to claim 1, wherein a wavelength selective mirror orwavelength selective filter that functions as the first wavelengthselector or second wavelength selector is disposed inside an opticalpath and is arranged from any among the group consisting of a gratingfilter, with which the refractive index is varied periodically in thelight propagation direction, a multilayer film filter, formed bylayering a plurality of sets of layers that differ in refractive index,and a photonic crystal, having a photonic bandgap.
 14. The opticalsignal amplifying triode according to claim 1, wherein the opticalsignal amplifying triode makes up an optical NAND gate, an optical NORgate, an optical flip-flop circuit, or an optical operational amplifier.15. The optical signal amplifying triode according to claim 1, whereinthe second wavelength selector selects, from among the light output fromthe second semiconductor optical amplifier element, an output light ofthe third wavelength that corresponds to the wavelength of the controllight and distributes the output light of the third wavelength among aplurality of optical transmission paths in accordance with thewavelength of the output light of the third wavelength.
 16. An opticalsignal transfer method of transferring an optical signal train, whichhas been transmitted via a predetermined transmission path, totransmission paths, among a plurality of transmission paths, thatcorrespond to routing information contained in the optical signal, theoptical signal transfer method comprising: an input step of inputtingthe optical signal train, to which the routing information have beenapplied, to the main optical signal amplifying triode unit; a wavelengthconversion step of supplying control light of wavelengths, correspondingto signals indicating the routing information, to the main opticalsignal amplifying triode unit, and making optical signals of thewavelengths of the control light be output from the main optical signalamplifying triode unit; and an optical distribution step of inputtingthe optical signals, output from the main optical signal amplifyingtriode unit, into an optical distributor and distributing the opticalsignals according to their wavelengths among the plurality of opticaltransmission paths connected to the optical distributor.
 17. The opticalsignal transfer method according to claim 16, wherein in the wavelengthconversion step, amplitude modulation using the control light is appliedto the optical signals, output from the main optical signal amplifyingtriode unit, to add new routing information to the optical signals. 18.The optical signal transfer method according to claim 16, wherein theoptical signal train is amplitude modulated at a modulation degree of nomore than 90%.
 19. An optical signal relay device, which, among opticalsignal transmission networks, transfers an optical signal train, havingrouting information added thereto by amplitude modulation, from onenetwork to transmission paths, among the transmission paths of anothernetwork, that correspond to the routing information contained in theoptical signal, comprising: a control light generator, generating, basedon the amplitude modulation signals of the optical signal train, controllight of wavelengths corresponding to the destinations indicated by theamplitude modulation signals; a main optical signal amplifying triodeunit, converting the optical signal train into an optical signal of thewavelengths of the control light; and an optical distributor,distributing the optical signal, output from the main optical signalamplifying triode unit, among a plurality of optical transmission pathsin accordance with the wavelengths of the optical signal.
 20. Theoptical signal relay device according to claim 19, further comprising anelectronic controller or an all-optical controller, which, in accordancewith the amplitude modulation signals contained in the optical signal,makes control light of wavelengths, which are in accordance with therouting information indicated by the amplitude modulation signals, begenerated from the control light generator.
 21. The optical signal relaydevice according to claim 20, further comprising: an optical splitter,branching a portion of the optical signal; a photoelectrical signalconverter, converting the optical signal branched by the opticalsplitter to an electrical signal and supplying the electrical signal tothe electronic controller; and an optical delay element, disposed at thedownstream side of the optical splitter and delaying the optical signalthat is to be input into the main optical signal amplifying triode unitupon passage through optical splitter; and wherein the electroniccontroller extracts the amplitude modulation signals contained in theoptical signal and makes control light of wavelengths, which are inaccordance with the routing information indicated by the amplitudemodulation signals, be generated from the control light generator. 22.The optical signal relay device according to claim 20, furthercomprising: an optical signal storage element, temporarily storing anoptical distributed from the optical signal distributor; and an opticalfeedback transmission path, feeding back the optical signal output fromthe optical signal storage element to the input side; and wherein whenthe optical signal is an optical packet signal that is to be storedtemporarily, the electronic controller makes a control optical signal,for converting the optical packet signal to a priorly set storagewavelength, be output, and the optical distributor distributes theoptical packet signal, after conversion to the storage wavelength, tothe optical signal storage element and makes the optical packet signalbe stored temporarily in the optical signal storage element.
 23. Theoptical signal relay device according to claim 22, wherein the opticalsignal storage element is equipped with a plurality of optical fibers,which are disposed in parallel and differ in optical propagation lengthin order to receive optical signals distributed by the opticaldistribution device, the electronic controller makes a control opticalsignal, for converting the optical packet signal to be storedtemporarily to a priorly set storage wavelength in accordance with thestorage time required of the optical packet signal, be output, and theoptical distributor distributes the optical packet signal, afterconversion to the storage wavelength, to an optical fiber among theplurality of optical fibers of the optical signal storage element andtemporarily stores the optical packet signal in the optical fiber. 24.The optical signal relay device according to claim 20, wherein theall-optical controller comprises: an optical coupler, branching aportion of the first input light; a continuous light source, generatingcontinuous light of the same wavelengths as the control light; anoptical coupler, multiplexing the continuous light from the continuouslight source with the portion of the first input light from the opticalcoupler; and a semiconductor optical amplifier, receiving the light fromthe optical coupler, outputting control light having the modulationsignals contained in the first input light, and being of slower responsespeed than the semiconductor optical amplifier.
 25. The optical signalrelay device according to claim 19, wherein when output light that arefrom the main optical signal amplifying triode unit are input, theoptical distributor selectively distributes the output light, which havebeen input, to optical transmission paths, among the plurality ofoptical transmission paths, that correspond to the wavelengths of thecontrol light.
 26. The optical signal relay device according to claim19, wherein the optical distributor is an array waveguide grating typesplitter, which comprises: a first slab waveguide, connected to an inputport; a second slab waveguide, connected to a plurality of output ports;and a plurality of array waveguides, disposed between the first slabwaveguide and the second slab waveguide and differing in length; anddistributes input light that has been input into the input port amongthe plurality of output ports according to the wavelengths of the inputlight.
 27. An optical signal storage device, storing an optical signalinput from an input optical transmission path and enabling taking out ofthe optical signal at an arbitrary time, comprising: a control lightgenerator, generating control light for converting the optical signalinput from the input optical transmission path to wavelengths, whichcorrespond to the transmission destinations contained in the inputsignal and are the same as or different from that of the optical signal;a main optical signal amplifying triode unit, receiving the opticalsignal that has been input and the control light and converting theoptical signal that has been input to optical signals of the wavelengthsof the control light; an optical distributor, distributing the opticalsignals, output from the main optical signal amplifying triode unit, inaccordance with the wavelengths of the optical signals; an opticalbuffer memory element, temporarily storing an optical signal of astorage wavelength that has been distributed by the optical distributor;an optical feedback transmission path, feeding back the optical signaloutput from the optical buffer memory element to the input opticaltransmission path to re-input the optical signal into the main opticalsignal amplifying triode unit; and an optical signal storage controlmeans, making the control light generator output control light forconversion of the optical signal, which is repeatedly circulated throughthe main optical signal amplifying triode unit, optical distributor,optical buffer memory element, and the optical feedback transmissionpath, to an output wavelength at the main optical signal amplifyingtriode unit.
 28. The optical signal storage device according to claim27, further comprising an optical signal gain control means, controllingthe optical signal, fed back by the optical feedback transmission path,or the control light supplied to the main optical signal amplifyingtriode unit in order to restrain the increase and decrease of the gainof the optical signal that is circulated.
 29. The optical signal storagedevice according to claim 28, wherein the main optical signal amplifyingtriode unit comprises: a first semiconductor optical amplifier, whichperforms conversion to a wavelength of a bias light and inversion of theoptical signal; and a second semiconductor optical amplifier, whichperforms conversion to the wavelength of the control light and inversionof the optical signal that has been inverted by the first semiconductoroptical amplifier; and the optical signal gain control means controlsthe optical signal, fed back to the optical feedback transmission path,based on the increase or decrease of the gain of the bias lightcontained in the output light from the second semiconductor opticalamplifier.
 30. The optical signal storage device according to claim 28,wherein the optical signal gain control means comprises: a first gaincontrol optical amplifier, receiving the bias light and a gain controllight, which is a continuous light of a wavelength that differs fromthat of the bias light, and outputs a gain control light, whichdecreases in gain in accompaniment with an increase of the gain of thebias light; and a second gain control optical amplifier, receiving theoutput light from the first gain control optical amplifier and theoptical signal, which is fed back by the optical feedback transmissionpath, and outputs an optical signal, which increases in gain inaccompaniment with a decrease of the gain of the gain control light. 31.The optical signal storage device according to claim 30, wherein eitheror each of the first gain control optical amplifier and second gaincontrol optical amplifier is arranged from an optical fiber amplifier oran optical waveguide amplifier into which a rare earth element is doped.32. The optical signal storage device according to claim 28, wherein theoptical signal gain control means comprises: an optical operationalcontroller, which controls the gain of the control light supplied to themain optical signal amplifying triode unit based on theincrease/decrease of the gain of the optical signal fed back by theoptical feedback transmission path in order to maintain fixed the gainof the optical signal that is circulated.
 33. The optical signal storagedevice according to claim 27, further comprising: an electroniccontroller, controlling the control light generator; a photoelectricsignal converter, converting the optical signal branched by the opticsplitter into an electrical signal and supplying the electrical signalto the electronic controller; and an optical delay element, disposed atthe downstream side of the optical splitter and delaying the opticalsignal that is to be input into the main optical signal amplifyingtriode unit upon passage through optical splitter; and wherein theelectronic controller makes the control light, for conversion of theoptical signal to the output wavelength, be generated from the controllight generator in response to an output timing indicated by storedsignal output information that is supplied from the exterior or iscontained in the optical signal.
 34. The optical signal storage deviceaccording to claim 27, further comprising an all-optical operationalcontroller, which makes the control light, for conversion of the opticalsignal to the output wavelength, be generated from the control lightgenerator in response to an output timing indicated by stored signaloutput information that is supplied from the exterior or is contained inthe optical signal.